I don't know what is wrong (or right) with me. I can spot reblues about every time, even in bad pictures. Same with re-nickel jobs.
At a gun show on Saturday, I spotted what looked, from 10 feet away, to be a nice full nickel S&W Baby Russian. When I had it in hand, it was obviously re-nickeled. I handed it back and the dealer asked if I wanted it. I said no, and that it was re-nickeled. He immediately denied that and informed me that the finish was original and that I didn't know much about guns.
Maybe not, but at the risk of helping the fakers and humpers, if you are going to polish a gun with a sideplate, polish the frame and sideplate together. Otherwise, you get a "dip" and even a gap where the sideplate meets the frame. The factory finish is perfectly flat, with no dip, and the gap will be almost invisible.
At another recent show, I saw a very nice Gen 1 SAA. I didn't even examine it closely, and asked the seller who did it. He didn't bother to deny the "restoral", just said he didn't know the restorer. There were two tip offs there - no calliber marking on the barrel, and small cylinder notches. The latter are very obvious and come about when the cylinder is turned down. The cylinder notches are a half-moon cut and when the cylinder diameter is reduced the length of the notches is reduced. That plus the excess gaps between the cylinder and the frame, show a turned cylinder and that makes the whole gun suspect.
Just a few tips on what to look for.