#2, always be skeptical. The paranoid may miss a sale every now and then, but the saying "the paranoid survive" is very true. If you really think this seller is selling a high quality product, and you want to go forward with the transaction, ask someone you two are both willing to trust to be an escrow. Some popular PuristSPro members have acted as an escrow in the past. The escrow takes the money from the buyer, takes the watch from the seller. Some escrows are also quite smart; they can confirm, the watch is in good condition. There was one time, being familiar with Patek 5960P watches, I knew sometimes the annual calendar could have a nearly undetectable problem. The problem is this; at the end of the month with less than 31 days, the watch would advance to the right date when the watch had the time advanced manually by the crown, but if you just left the watch on a winder, it wouldn't advance to the right date (it'd go to 31 on a month with only 30 days, it should go to the 1st of the next month). So I mentioned this in my report that I noticed when I had the watch for a few days.
Of course! The escrow needs to be a trusted individual! After all, the escrow could disappear with both the money and the watch! That'd be terrible!
The escrow will also look at the paperwork and the serial number on the watch to see if there's anything "obviously wrong" and will help you identify any obvious problems. If the watch is an obvious fake, the escrow should have the expertise to recognize it. If it's a genuine Rolex but with some fake modifications, the escrow may not always recognize it. Mainly, more obvious things. The escrow will check if the watch keeps reasonable time (+/- a few seconds a day), the escrow can confirm the box is present, the escrow should know what kind of paperwork and accessories (screwdrivers, extra strap, booklets) comes with the watch to ensure it's all there, and condition of the watch will all be accurately conveyed.
It's also best to find an escrow who is a watch person who is familiar with the brand of watch you're buying. So let's say you're trying to buy a Panerai, don't go to an escrow who's a Patek Philippe expert but knows nothing about Panerais.
Adding in an escrow service is obviously time consuming. But it does add a layer of protection. It's not entirely foolproof, but at least you can do your due diligence.
Escrow limitations; 1, if the seller is really trying to trick an escrow, it's possible; 2, an escrow cannot usually tell if a watch has been stolen (the escrow doesn't maintain a comprehensive database), the buyer should take the serial number and check it with the manufacture's database and Interpolice database; 3, most of the time, an escrow does not open a watch unless something specifically needs to be confirmed, most buyers and sellers both don't want a watch opened unnecessarily, but not opening the watch has its caveats (I would tell the escrow to not open a watch unless they notice something extremely unusual or suspicious, like significant moisture damage on the hands/dial, then I want to see the movement); 4, the escrow could be crooked and take both the money and the watch and "disappear" so it's important to get someone you can trust!