There is no universal rule for who pays for a status search. In a private sale, a small fee can be negotiated as part of due diligence. The more important point is that the search should use the physical watch's serial and the buyer should see the dated result directly.
A seller-paid search can still be transparent
The seller can order it and share the original report, provided the buyer can verify the serial, timestamp, and provider's scope. A cropped image or verbal assurance is harder to assess.
A buyer-paid search gives direct control
The buyer may prefer to enter the serial and receive the result themselves. This avoids uncertainty about which number was searched, though it does not change the database's coverage or limitations.
Agree on the process before paying
Put the serial-verification step, inspection, payment timing, and return conditions in writing. A responsible seller should allow a reasonable check before funds become difficult to recover.
If the parties disagree over a modest check or the seller demands payment first, weigh that against the transaction value and be willing to leave.
Run a Dated Search
Use the confirmed serial and keep the full result with the sale record.