Hi Elton.
1.
Mostly, the site is not for selling anything. Sandi is right, there is one forum with "Classified Ads", and they do have occasional "group buys".
2.
Also, many people are willing to trade plants, cuttings or seeds. Some will give them away for postage, but it is smart, before asking for favors, to have offered some freebies of your own. If you find specific plant varieties in the Plant Database that you want (or have and are willing to trade or give away), check the "Have / Want Lists" for that variety.
We occasionally have seed swaps, and once had a plant swap, run through Dave's "Goodie" feature "Seed Swaps". (See the far-left blue menu bar for "seed swaps".)
3.
Also, we have a list of vendors called "The Green Pages" (far-left blue menu bar). You will see recommendations for some of them, but we don't really solicit negative reviews.
4.
What I would do to try to find "the best" vendors is to go to a forum matching my interests (like "daylily" or "roses"). Start a thread (or search, and find an old related thread) like "where do YOU buy your XYZs?" Such a thread would be one good place to offer some trades.
It's always effective to show that you have done some research already, and state what you're most specifically interested in, when trying to get suggestions. People are more willing to put work into an answer if the question shows prior thought and effort.