I purchase most of my coins through ebay. Luckily only a couple of duds in hundreds slipped through the net, as you said, the ones with blurry pictures. I even had an undated 20p with the date filed off!! So stay away from dodgy pictures and go with sellers with good feedback and clear pictures. Whether the seller states he accepts returns or not, under ebay policy if your not happy it can be returned.
As 1967 states in the previous post, if your looking for a high end coin, its maybe worth looking elsewhere if it at all looks suspect.