07 f2p & p2p

Not sure what people mean when they say "buy in p2p and sell in p2p"
(Just read that in a merchanting discussion thread in this forum, also seen it several other times)
In order to play 07 you must have membership..so everyone is p2p..if items are "more expensive" in f2p why wouldn't you just go to a p2p world and buy them? Am I missing something?

 

Was the guide you read a recent one? This used to be an effective method before 07 but as you said, anybody that can access the f2p servers can also access the p2p servers.