It's really not too difficult once you've seen a few. When I first got on B&B I bought a two razors on ebay that were in excellent shape. It was only later that I realized they had been replated. I don't mind replated razors but it's always nice to know beforehand, and I don't think that they should command the same price as a mint unplated one. Too me that's where the dishonesty comes in. If there's a nice razor on ebay that you're not sure about, go ahead and PM the seller before you bid on it and hopefully they will be forthright about the razor's condition.
+1 The replated razors look nice, and that doesn't mean that somebody isn't interested in buying one, but I think it should be stated.