I have no problems buying off Ebay - but there are some pretty obvious pointers to condition:

Out of focus photographs are hard to produce with modern digital cameras so if the photos ARE out of focus, the seller is hiding something.
Even someone completely ignorant of cameras can tell if knobs turn and buttons press - if they won't tell you so, either the knobs don't turn or the buttons don't press.
Someone who has listed several 'faults' has probably listed them all (and a fifty-year-old camera like I buy WILL have faults).

I have only once bought a camera off Ebay that was nothing like as described and that went back for a full refund. I have also bought cameras that were not quite as described and I have actually sold those again on Ebay for more by accurately describing them.