Pre-paint photos are nice but seldom seen. Sellers at least admitting the bike is a repaint instead of trying to pass it off as original is a good thing.
I asked a similar question here about one of my bikes several years back. After posting up a few pics, a board member I had great respect for said he'd leave it. Considering it is somewhat of a rare bike, I took that advice. I did touch up the paint, to keep it from deteriorating from the elements.
In another case, I am about to take delivery of another bicycle which has been repainted, and has all original parts. The seller is very well respected. He and his business partner do an excellent job finding old rare road bikes and reconditioning them.
In my opinion there really isn't a correct answer to the paint/leave original debate.