A hard one to nail precisely, but it looks like it could be a black-dialled variant of the 2403 as shown in this '30s catalogue:

The narrow shield and lack of Heuer stamping put it earlier than the 40s-50s the seller states - those are indicative of the 1930s for me. The 5 digit serial in that sort of range is indicative of a 30s watch too, prior to adopting 6-figure serials at some point during, or possibly immediately after, WWII. I note that it has round pushers, which if the case is original is both quite unusual for Heuer at the time and the watch could not date from before 1939, as that was when Heuer introduced their first waterproof wristwatch case.

So I can't be definitive one way or the other, the case has been refinished and crown replaced so hard to tell whether it's original as a whole, but the dial looks right, movement is period correct, serial number could be in the right sort of range... Could be worth a punt at the current bidding levels at least.