I'm the same, I wouldn't buy something off someone with just the one post without some more proof of sorts, detailed photo's and all that. However I'm not one for banning or locking part of the forum, one of the pro's of this forum is its openness, if you see someone selling something it is up to the buyer to make sure the part is there, through pictures or a phone call to the person or something like that, we live in a society where the buyer assumes the risk. I think everyone on here is smart enough to check what they are buying and who off. One time I bought off someone who was relatively new (in another forum) and got them to advertise it on ebay so I could buy through there (I footed the fee's) but it made me more comfortable with the purchase.
And as 555wagon says lots of people view and don't post for various reasons. With my last car it took me a year to get 100 posts on a forum and that was just because I was learning lots from just reading, the tutorials to follow, my car didn't break, and I was unsure how people would react to a seemingly stupid question.