When two collectors swap watches, each person becomes the recipient of a different piece. A search on one serial tells you nothing about the other. Treat the exchange as two individual transactions and check both watches before handover.
Write down what each side is offering
Record the brand, model, serial, condition, included parts, and agreed value for each watch. Compare the serial on the watch with that side's documents. If a bracelet hides an identifier, plan a safe inspection before the meeting.
Run two searches and keep them separate
Search each verified serial and save the date and result with the matching watch file. A no-match for Watch A does not clear Watch B. If either serial returns a report, pause the entire exchange until you understand what it refers to.
Document the exchange
Sign an exchange receipt listing both parties, both serials, each watch's condition, and any cash difference. Keep copies of the messages and results. If you later discover an identifier differs, you can show exactly what each person transferred.
Authentication, condition, and reported theft are separate checks. Arrange a specialist inspection when those questions matter; a database result cannot assess a movement or the value of the trade.
Check Both Watches
Run one serial search for each piece and label the results clearly.