I believe that the most important traits of a great mentor are:

1. Willingness to learn: knowing that one does not know everything, and is capable of being wrong, even as a mentor.
2. Shared vision: in pursuit of the similar goals in life and work.

Unfortunately, these are not discernible without personal experience with a given mentor, since preaching such traits is not the same as practicing them.

My response is heavily biased towards web applications, and in-browser bug reporting, though some tools may allow native iOS and Android implementations, as well.

The answer depends on on the type of audience that needs to report bugs: private and targeted (developers, employees, etc.) or public and open (all website visitors).

Private group typically have some level of vested interest in reporting bugs, and may have higher tolerance for user experience (UX) issues associated with the bug capturing process; public groups, however, need much more streamlined tools and less hurdles in order to encourage bug reporting.

FOR PRIVATE GROUPS, the top two tools that we have used, may be a bit too complex for public groups, though they can integrate with more user-friendly tools. Both of them also allow annotations on the screenshots that they take.

https://getmarker.io/pricing
MARKER starting at about $25 per month is the cheaper of the two. It integrates with some tools such as Trello, Jira, GitHub and Slack, and they have plans for integration with HipChat, which may make it more user-friendly for the public group.

https://usersnap.com/pricing
USERSNAP starting at about $80 per month is more expensive, but has more features and certainly more integrations out of the box.

FOR USE WITH PUBLIC GROUPS, I recommend using a chat service, with built-in screenshot capturing, since those generally seem more user-friendly, and have less complexity in the capturing phase, and have an established use pattern. Of course, some of these make great tools even for more private audience groups, as they can be limited to such groups easily using some basic server-side coding.

https://doorbell.io/pricing
DOORBELL.IO that has a free plan, supports screenshots. and is one that we have not used, but seems simple, very promising, quite open. It is also highly malleable due to having an API for integrating it into your own widgets, and supporting "web hooks" which may be used to post content from it to any web address.

https://www.olark.com/pricing
OLARK that also has a free plan, is one that we have used extensively, since it has a co-browsing feature. Once initiated by the chat operator and accepted by the visitor, it provides a live feed into the visitor's browser.

NOTE: We have been an Olark partner for a while now, though I am writing without bias, and have NOT included our referral link in this response.

Since some new business owners get excited about revenue, instead of gross profit, it is always wise to show the difference.

Let us consider as an example, that your business makes $10,000 (revenue) in revenue in one month, and has a cost of goods (or services rendered) of $7,000. This means that you have to pay someone (e.g. a vendor) $7,000 to make $10,000.

Then, you are faced with general expenses for the month that amount to $2,000 (utilities, etc.).

The excerpts that you quoted from the article mean that you should NOT think that you are spending $2,000 from the $10,000 (revenue), but that you are spending $2,000 from the $3,000 (gross profit: $10,000 - $7,000).

As you can imagine, you will be much more cautious when you realize that you are spending 66% of your gross profit on expenses, and not simply 20% of your revenue.

While this is certainly common sense, the reason for his pointing it out is that sometimes people do not keep it in mind.

[This is a duplicate of the question at https://clarity.fm/questions/4300]

Since some new business owners get excited about revenue, instead of gross profit, it is always wise to show the difference.

Let us consider as an example, that your business makes $10,000 (revenue) in revenue in one month, and has a cost of goods (or services rendered) of $7,000. This means that you have to pay someone (e.g. a vendor) $7,000 to make $10,000.

Then, you are faced with general expenses for the month that amount to $2,000 (utilities, etc.).

The excerpts that you quoted from the article mean that you should NOT think that you are spending $2,000 from the $10,000 (revenue), but that you are spending $2,000 from the $3,000 (gross profit: $10,000 - $7,000).

As you can imagine, you will be much more cautious when you realize that you are spending 66% of your gross profit on expenses, and not simply 20% of your revenue.

While this is certainly common sense, the reason for his pointing it out is that sometimes people do not keep it in mind.

Tying your compensation to your performance can not only increase your revenue stream, but also your chances of closing new deals.

Instead of replacing your pricing model, you can keep your current monthly rate, but add one or more of the pricing models discussed below. This should not endanger the closing of a deal, since the performance-based portion of the price not only conveys confidence and honesty while limiting the client's financial exposure, but also makes the fixed (e.g. monthly rate) portion look like a good deal because it gets viewed as only a portion of the total cost.

Furthermore, doing so will encourage you to keep offering more value, since more value (not just more work) will translate to more revenue.

Over the years, I have dealt with many advertising agencies as well as providers of advertising tools. Some typical pricing models from my experience are listed below. Not all apply to every situation: some are good for e-commerce and other advertising campaigns that are directly tied to revenue, others are more suitable for advertising efforts less directly connected to revenue, e.g. publicity campaigns, some social media work, etc. I have tried to detail them here, but if you have any questions, I am happy to discuss them on a call, or in this thread.

GROSS PROFIT SHARE:
The agency takes a share of their gross profit, which means that it would pay attention to advertising products and services with higher margin, and allocate advertising funds accordingly. This can be tracked by asking the client to assign a gross profit margin to each product/service that the agency helps advertise; then the agency takes a set percentage of that profit. Essentially is like a revenue share agreement, but a variable commission, based on profitability of each product or service for the client, as follows:

Formula: Item revenue x item profit margin x agency's rate = agency income

For example, the agency shifts spending to campaigns for product A and those like it, because:
Product A: $1000 x 50% x 15% = $1000 x .5 x .15 = $75
Product B: $1000 x 10% x 15% = $1000 x .1 x .15 = $15

With larger accounts, it is possible to have a profit share that goes beyond just gross profit, but that is a dangerous territory for an agency, unless its relationship with the client is well established, since even more things that are out of the agency's control can reduce the amount of such profits.

REVENUE SHARE:
This works just as a profit share agreement does, but is much more common, and certainly easier to track. Since the agency only takes a percentage of the revenue that its advertising produces, regardless of what the profit margin is.

PAY PER ACTION/LEAD/ETC.:
The agency sets a price that it collects per conversion, which it should track using web, call and other analytic software. The further down the pipeline the conversion, the higher the agency can charge for it. For example the price of a regular website form lead, can be far higher if the provided phone number is answered when called back. Some advertising services make tracking this easier than others, e.g. Google AdWords Call Tracking https://support.google.com/adwords/answer/6100664?hl=en.

BONUS FOR MILESTONES:
It is possible for an agency to set arbitrary or rational milestones for receiving bonus payments, e.g. certain level of revenue generated for the client, or certain level of social media clout/followers/etc. achieved.

COST PERCENTAGE:
By far my least favourite, some large providers that offer tools to centralize advertising campaigns, as well as some advertising agencies, charge a percentage of the advertising expenditure (Ad Spend). From a client's perspective, the more they spend on advertising campaigns, the more they must pay the agency, regardless of the level of success achieved by those campaigns.

As Humberto stated, it should be easy; but depending on the complexity of the design, and how well it is implemented in the application, it could be longer: the worse the implementation (more probable for lower quality apps), the longer it will take.

Therefore, if the app itself is well-designed and follows best practices, the cost should be relatively low at about an hour or two.

However, this does not take into account ancillary work needed to re-publish the new app, which itself could take an hour, two, or more, depending on the issues that may arise.