I don't know about other expensive watch brands.
But it is certainly NOT the case with Patek Philippe watches. Each and every piece of PP watch produced by the company since the first piece of watch was produced in 1844 are registered in PP's database in Geneva. They have in their database the owners' names, addresses, etc... of all the PP timepieces the company has ever produced.
Same for Rolex as well.
All an authorized Patek Phillipe dealer has to do to find out if a PP timepiece brought in by an owner is real or fake is to confirm the owner's name & address with Patek Phillippe Company's database along with the watch's model number, case number, serial number, and movement number and they should be able to confirm if the watch is real or fake. The dealer will certainly ask to see a photo ID to confirm the owner's identity.
Same for Rolex.
Patek only produces about 40,000 timepieces a year for the global market. Whereas, Rolex produces about 1M pieces a year. All Patek timepieces are handcrafted. Whereas most Rolex timepieces are mass produced except the very high end timepieces paved and encrusted with diamonds that are handcrafted.
All rolex timepieces are handcrafted as well. They maybe produced in higher quantity then PPs but they are individually handcrafted. Some models, not just the diamond, gold/silver version takes up to year for it to be handcrafted.
That's why Patek timepieces are so much more exclusive because they are so much rarer and so much harder to get. Just because someone has money doesn't necessarily mean that he can go to an authorized Patek dealer and get a new Patek timepiece right away. In most cases, there's only (1) piece available amongst all the authorized Patek dealers in Singapore if he is looking for a specific model number priced at the low end or mid-range category.
Actually, the low-mid end Patek's are Eta movements, you might want to avoid those, while Rolex low end is its own.
As for Patek's very high end timepieces (grand complication watches), he will need to special order and it can take up to 3 years for Patek to make the watch. Each piece cost between $250K to $2.5M depending on the model number, materials used, and how complicated it is. And they only produce a few pieces a year for each model of their very high end timepieces.
If you have the cash, why not. Problem is, most people haven't even heard of it or could afford, from the sounds of it, you don't either.
Most Patek owners convert their watches to cash at auction houses like Christie's, Sotheby's, or Antiquorum. Instead of pawning them at pawnshops like Rolex owners.