"Out the door" = the tax, title, and license fees are baked into the final price already. The buyer still pays it but it's hidden. Or you could say the seller pays it if he forgot to mark the item up, or he's discounting it a convenient amount to get it to move.
Pay the $20 and get it over with, IMHO. Everybody will feel better, especially you. Unless you are counting on the manager refusing the extra $20 when you buy the Mak.
ETA: not trying to insinuate anything, that's just the only reason I can think of to *not* just return the 20. If you wait too long, any good will is lost.