In the fight against unscrupulous and bad ebayers, I'd like to call to everyone's attention this particular tool:
www.toolhaus.org it filters out the positive feebacks allowing you to see all the bad and the neutral, as well as mutually withdrawn. I think it provides another useful layer of info about potential bad sellers.
I agree with Bill about commong sense. Often I ask myself, shouldn't this be in a museum? and if so, why is this guy selling it cheap when any dealer or museum would pay handsomely for it. And of course, look at how many of them are being sold. If I see 10 "rare, unique...whatnot" I keep some cheerful suspicion.
Emanuel