If the seller Y is identifiable but simply abroad, then there are various cross-country agreements that would allow to use the legal process in their country to

If the seller Y is identifiable but simply abroad, then there are various cross-country agreements that would allow to use the legal process in their country to collect money from them in various ways, especially if there's a lot of money at stake - like the $10M discussed in the article. If the seller is unidentified, then it is possible to get a judgement and work on identifying them. If it's not just a civil dispute but felony fraud, then law enforcement might identify them some years later, it happens. Of course, if everyone involved is properly anonymous then it's very, very hard to enforce anything, and takes enough effort and money so that it's not worth the hassle for small amounts, so for that there's simply some 'caveat emptor' in dealing with foreign anonymnous sellers. If you defraud $10 off of someone across the ocean, you are likely to get away with this. But for large cases of fraud? Everyone makes mistakes now and them that may allow them to get identified, and such fraud can be prosecuted many years later.