I have worked on a B2B marketplace for technology and advised for a few B2B vertical marketplaces as well. This was for different clients in US, Asia and Middle East.
You will need:
1. ability to attract integrators and sellers
2. Easy onboarding
3. Low listing fees
4. Great marketing team
5. A compelling reason to adopt your marketplace instead of alternative options and "current ways of doing business".

If you have these, your traffic will start growing, which would lead to signups and so on.

Multisided Platforms have the chicken and egg problem, to build them, in the beginning, you need to do things that don't scale:
1- Go to the most difficult side (users) to adopt the marketplace and make them a demo. ex: buyers
2 - Ask them what they need to buy
3 - Then go look for the sellers of what they need and onboard them and call the buyers...
4 - Do this before you start too much coding...you will need to do the old way without tech or just with basic MVP, to understand if they need your product
5 - You validate the idea while you speak directly with all sides, and can improve the product with their feedback.

Only quick tips that are coming to my mind are based on the digital B2B marketplace are as follows:
1. Persuasive communication – selling (professional selling) – has a complex job to do it must inform, persuade, and differentiate. While nothing about selling is itself intellectually taxing, and much of what makes it work is common sense, it needs careful orchestrating, and any complexity is created by the fact that many aspects of the process need deploying accurately and in parallel.
2. Selling is inherently fragile. By this I mean that it is sensitive to small change: something done a little differently can make the difference between agreement and rejection. Details matter: even a poor choice of a few key words of description can affect the outcome.
3. Selling must be acceptable to the client. There is a fear among some that too strong (“pushy”) an approach is incompatible with projecting a professional image, and indeed it could be so. Well considered sales approaches, however, can help create, retain, and even enhance, the professional relationship that you are at pains to work within.
4. Selling must be deployed in a tailored manner. There are certainly principles to be borne in mind, but there is no one right way to sell. We can all spend a lifetime learning to adapt better and better to changing conditions and, not least, client demands and expectations. What is necessary is to sell in the best way – whatever that is – every time, meeting by meeting, client by client approaches must be well matched to the circumstances.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath

Hello. I help increase sales through customer success.

I quote below my answer to a similar 'business strategy' question. This outlines an approach. We can talk about your specific need and solution. Let me know. All the best - Somesh

"Business Strategy: In a two sided service marketplace for freelancers what should be the Go-to strategy or the best way to reach the target audience ?

Somesh Bhagat, Increasing sales through customer success answered:

Hi.

My expertise is in helping expedite business outcomes.

The best advise is to tell your prospects of the unique value of your service or its unique positioning in terms of how it will help your customers. You need to articulate compelling propositions that are irresistible and sustainable. It should be better than your competition and communicated strongly.

A two sided service market place it a tough spot. You have to address two big audiences, who may have totally different characteristics, messaging need, and business development strategies.

Before your Go-to strategy you need a compelling story, a mission, and a vision. You also need to articulate a business strategy encompassing both ends of your business model.

The go-to strategy will evolve from your business propositions, market, business model, and audiences. What kind of freelancers you are taking about - professionals, technicians, labor et al. Who is on the other side of the market place - individuals, households, businesses-small/medium/large/government et al. What is your revenue model and business plan. How strong is your competition? How strong are you versus competition? Do you want to go for the whole market or a niche depending upon your SWOT? How are you different from Fiverr, Upwork, Clarity, and the like or unlike? Your go-to strategy should answer all these questions at the very least.

You may find better and sustainable success going this route.

Hope this helps and let me know if I can be of further assistance for the above. Best wishes."