Bill of sale

A bill of sale is a document recording the transfer of a watch from seller to buyer, typically showing the parties, the watch and its serial, the price, and the date.

For a dealer buying from the public, it's a core record: it documents what you bought and from whom, supports your cost of goods at tax time, and helps if the watch's ownership is ever questioned.

Use one for every purchase, keep a copy with the watch's records, and make sure it identifies the watch by its serial number.