Buy it Now, Offers, and Commission

Just wondering where, if anywhere, I can find options that can give me these sorts of abilities? Or will I have to code these separately or have them coded separately?

Basically I just want a set price, and other users can send in offers, which the auction owner can accept or reject.

Also wondering if there’s an option which, upon payment, takes out a certain percentage of a successful sale. Although I may have all payments pass through me, so I could just do it at that time.