I'll normally touch-up a painting after selling it, and sometimes this touch-up becomes pretty extensive. I know it isn't necessary, but I feel better for having delivered a better product. Unfortunately I can't always find the time to scan the revised painting, so many times only the purchaser knows what the final, completed painting actually looks like.
This morning I noticed that someone posted my original Mancow unicorn painting to a site called Expressobeans. Luckily I saved a scanned image of the revised version, which for a larger painting normally takes two scans which I then stitch together in Photoshop to create the online image.