I think it is complicated. If it is a stamp, you either find another, or live with it. If it is a pasted snipe, it kind of depends on whether the snipe enhances the history of the poster and whether the snipe is removable. If the snipe is removable with some effort and the poster price suffered because of the snipe, then it is probably best to try and remove it. If it sold for near market price, than exchanging for a better one or simply waiting is the better choice. That American Graffiti one I showed sold for $70-100 less than other recent sales and is in pretty good shape other than the snipes. Worth it to me to carefully remove them.