I don't think this is a case of someone being stupid enough to pay thousands of dollars for nearly worthless stamps.
More likely it is being done for its humor value, or for money laundering.
Looking at some of these from the list of sold US stamps sorted by price on
ebay, these all have the same MO:
1. The seller has a new
ebay account.
2. A common stamp is listed with a ridiculous price
3. Location of stamp is always a different city, as if it was chosen at random.
4. Item is always bought through a "best offer accepted" method.
5. Some of the sellers have other items for sale, some at more reasonable prices.
The best offer that was accepted could have been $.01. You could try that, offer one of them a penny and see what happens. I'm not going there as I don't want to be stuck with the postage. You could keep the joke going by having it shipped registered and insured. You could brag that you bought a $10,000 stamp on
ebay for a penny. Some people find that sort of thing funny.
Or it could be money laundering. How effective that would be in this case is not clear. In money laundering, you have a stash of stolen or ill-gotten money you want to get in your bank account without arousing suspicion. Setting-up
ebay transactions taking money from your illicit account into your legit account could be a laundering technique, but as all these transactions are electronic, it still seems it would be pretty easy to trace.
So I vote such listings and transactions are jokes. They made us wonder what was going on.