Vintage unknown Deville

Looks legit and the case appears to be gold. Poor photo, but appears to say 14K. The crown is damaged, but otherwise it looks pretty good.

Here's some advice from someone who has bought a lot of watches in person, but also sometimes missed out. If you like it, don't dawdle and ask too many questions, just make an offer and try to buy it. You don't need to know the reference number and the seller can't open the case. If he has it opened by a watchmaker, sees that it's solid gold, and gets more information, the price may go up.

You can get the reference number later. If you wait or do too much research for the seller, someone else may buy it, or the seller will get other thoughts about it. He may even be reading this thread.