"Because the current rules are unclear how?"
Well for a start there is three stickies. The selling and the hosting stickies are needed, but I propose you change the new "Save Yourselves A Lot of Hassles" sticky be converted into clear guidance if you wish to buy from the forum.
At present there is no guide on how to buy with proper etiqute.
And if there was, with a banning warning on people who break these guidelines, they'd be less of a "dibs, ask questions, sort out the money later , can't, nevermind attitude.
Just a suggestion.