Looks like everyone is going for the idea
Hi Lucy, you're right. There are plenty that are skipping the selling themselves and going for the platforms to attract the sellers as their business model, it's becoming so popular that their is an industry built around making auction sites to sell.
Most people I've seen in the past that have these sites have grand plans of taking over the universe, but in reality, unless someone has a massive budget and a cast of dozens, making any serious impact in the market is very difficult.
Everyone will complain about eBay, but most will still use it for one very simple reason..... it's effective. It's effective because it delivers traffic, and traffic is what sellers want to see!
I still see possibilities for small fledgling sites like yours, not on a massive scale, but on a much smaller local scale. For example, if you live in town, aim it at your town. Create a business services directory in there for local business, talk to local charities about listing their products there and so on. Talk to local supermarkets about listing their weekly specials and a few special offers for site users only.
There is dozens of things you can do to widen the platform of the site and generate traffic through other avenues that can then be used to create interest from sellers, even just locally based ones.
Aiming at a local level can get you a lot of support, for minimum outlay, and then who knows where you can take it from there. Maybe get the local newspaper behind you, offer them editorial space, do things that create enough interest to generate visitors, and that doesn't have to be by selling products themselves initially.
You have the basics in play, but now you have to get creative to make it work for you. If you fall into the trap of just thinking sellers will flock, that can be a very early end unfortunately.
Good luck with it.