Here are my thoughts :
1. If a frame sells during "high season" on ebay (roughly late Feb - June);
2. If the frame is well advertised with good pictures and an auction of at least 5-7 days;
3. If the frame uses current threading and seatpost standards;
4. If the frame and fork sell for less than ~$100 + shipping and it's Reynold 531 throughout;
Then it's probably in bad enough shape that it's o.k. to repaint the bike under any circumstances. At least, this is the approach I have taken when selecting a bike to purchase with a repaint in mind.
Now let's hear the exceptions !!
- Don Gillies
San Diego, CA