multi vendor shopping system

[byronyasgur]

anyone know of a system that allows multiple vendors to sell products on the same site
eg

vendor 1 lists product a in category x
vendor 2 lists product b in category x
vendor 3 lists product c in category x

buyer searches category x and finds
product a, b and c

choses product b and pays vendor 2 via the site

i think that there will need to be some kind of escrow service involved either operated by the site owners or a third party if such a thing is available/possible

anything remotely close would be of help - however a multi shop system is not really what im looking for - the vendors would often be only selling a single item and there could be many sellers


thanks

edit: actually i just found x-cart pro - has anyone any experience of this in multi-vendor mode and any opinions etc