Don't set it in stone
Do not write an inscription in a book (put your message in a card) unless you are 100% sure the recipient doesn't have it already. This way, at least they have a chance of exchanging it for something they don't have already. (This rule applies particularly to the early bird shoppers mentioned above.)

Can I get a price check?
Always, always make sure the price tag is nowhere to be found on your gift. It's just plain tacky.

Happy Hunting and Happy Holidays!