[ghthor]

In this area I see the only real defence coming from employing the users to build graphs and small knit communities. If you empowered your users with data and suggestions you can leave it up to them to build a web of trust for the users that are providing the stated service or at least goals of the community. This leaves an open hole for the community of cheapest made knockoff products a place to grow as well.

In this environment new sellers are handed nothing with a mountain to climb, but you could offer a series of incentives to encourage the sellers within the webs of trust to review and verify new sellers. You could encourage sellers to meeing within meatspace as well to build these webs of trust. This would allow new users to join communities of trusted sellers/makers and then be given the proper showcasing and search placements to the buyers.

The TL:DR use your real community and encourage it to grow outside the site and within meatspace to build webs of trusted sellers and makers.