It’s a good idea but probably difficult to implement and police.
The problem with taking the restrictive standard approach that tomthumb previously suggested, ie
it is self policing really.
only buy from people with long history, only buy from people whose name you know from the bike/ chat forum. don’t buy form people whose history looks like this
£
£
£
£
£
…is that none of that is clearly defined. How long is long enough? How can I tell if I ‘know’ somebody? What’s wrong with buying from people who only sell if you have a good transaction and get the goods you want at the agreed price?
I don’t post much on STW but recently I sold an On-One Il Pompino on here and the buyer went to the trouble of starting a +ve rant thread to say how chuffed he was with the bike and the efforts I made to get it to him in one piece.
Just use care and common sense.