Also, for those of us who aren't experts: Are there clues to help you identify whether a dial has been retouched or not? That is, other than a very vintage dial being in "too good to be true" condition?
Too good to be true or incorrect details are two ways to do it by just eyeballing. If you actually have the watch, a couple of other tells are refinishers will often put a notch in the edge of a dial at 3:00 as a marker to keep the orientation correct. If you remove the dial, refinishers often scratch codes or something on the back of the dial.
Cary's remarks are of course spot on, particularly with the brands he mentioned, and extra particularly for Rolex for the reasons mentioned.
But I also think for some brands, it's not such an issue. Hamilton collectors seem to be very okay with refinished dials, perhaps partly because there's a good source (International Dial) for mostly correct refinishes. And my brand of choice, Gruen, used hard-fired inlaid enamel print for many years. When these dials are refinished, they aren't even reprinted. Just stripped, cleaned, polished and given a fresh clear coat. With few exceptions, they come out perfect, like new.
A really nice original dial is probably always more valuable than a refinish. But most dials haven't survived in nice condition. Personally, I'd prefer a correct, clean refinish over a ratty original.