Great question! I assume the listing owners (the folks paying the monthly fee) are the trainers? Here are my thoughts, in no particular order:

1) I googled FitnessSpot, and found a large number of results. I'm not sure if FS is a website, or a local club in Michigan, a studio in NYC, or something else entirely. A little SEO will go a long way; along with some brand building activities. Get your name out there in multiple channels, make sure you dominate the search results.

2) I'm assuming you're a startup. At this stage, the name of the game is users. If you have a large user base, trainers will pay to get access to them. If you a lot of trainers, users can still use the phone book or google to find them. The key is user enrollment; and that's driven by traffic.

3) Is your value as a matchmaking service for trainers and their clients? That seems like a one and done activity- client meets trainer, trainer meets client; they both leave the site. There are a couple of options here- you can continue down this track, which is fine; but looking for either trainer or client to be a long-term revenue stream seems....limited (at best). In this case, I would recommend exploring other revenue streams - maybe adsense, maybe affiliate marketing. In any event, the name of the game here is still traffic & brand awareness. Think of a comparison to a dating website- by its very nature, if you are doing a good job, your users will fall out of the marketplace.
You could also look to drive more engaged users. This is likely my recommendation (without knowing many specifics). In this case, you'll need to think of other value you provide. Is it tips & tricks, nutritional information, exercise of the day, etc.? The point is that you would need a much smaller user base to drive the same amount of traffic. Your efforts can be less focused on relentlessly attracting new users, and more focused on building an online community. It's under this model that you'd be more likely to monetize the users/trainers directly; but keep in mind what they're paying for- users will pay for valuable content; trainers will pay for access to the users.

I'd love to discuss this with you in more detail, and better understand if I can help. Please drop me a line at your convenience to chat. Cheers!

How much does the 30% increase in profits equal? In order to set your pricing; my advice is to meet with the client & map out the objective. You'll need to understand how big an impact you can really have & how you will help them achieve that benefit.
For example, if you're going to be able to move the needle from $1,000 to $1,300 per month, you've increased profits by 30%, but the business just won't be able to pay you very much. However, if you can go from $1MM/mo to $1.3MM/mo, that's a very different story. How long will that benefit last? Is it a permanent solution, or will the client only get a few months benefit before their competitors begin doing the same?
All of that said- the amount of time it will take to for either client could be very, very different.

Always charge based on creation of value; Never charge for a consultation; Always make sure you take the time up front to understand what you can do for the client; THEN (and only then) do you start to come up with a price quote.

I'd need a few more specifics to say (especially around your industry, whether or not you're already established, etc.), but-
It usually comes down to reputation and relationships. I'm assuming that this is some sort of service business (consulting or information management? I'm not sure what else would have 'research' as the only barrier to entry.)

The key is to not make your product a commodity. Differentiate it. Make sure you're providing a quality product, and that your clients/customers are receiving value for their cost. If it's worth it to them, they'll come back.
Make sure you focus on their experience, make it a good one, and don't give them a reason to look at your competitors.

I'm inclined to agree with the other posters here that social media COULD be an avenue to explore. That said- are you in an urban market, or somewhere a bit more rural? The auto industry can encompass a great many things- are you creating and selling new parts, or are you offering a detailing service, or anything on the very wide spectrum in between?
My point is that there are likely quite a few avenues that will be much more productive than email and cold calling. Check for local trade events (Google is a good resource for that). For less money than you're probably spending on emails, you might be able to get a table and display board at a nearby exhibition. A weekend of face-to-face time with decision makers goes a long way. You could have opportunity to get in front of some local media (the news loves 'soft' stories about new businesses in the neighborhood). You might even be able to offer a sample, similar to a portfolio or proof of concept. The key is to find a way to differentiate yourself. You don't need their attention for long, but you do need to get their attention.

Give me a call- I'd love to discuss this with you in more detail.