At least in the U.S., anyone can look up all the patents a person/entity owns. So, your fraud wouldn’t get very far.
https://assignment.uspto.gov/patent/index.html#/patent/searc...
https://assignment.uspto.gov/patent/index.html#/patent/searc...
It’s like someone selling a deed to land they don’t own, or leasing a property they don’t own to a tenant.
Few people will even bother to try, and if so, you keep them at a distance with some random bullshit (communication can break down _sooo_ easily), but it certainly poisons the well by adding a layer of FUD to the tech you're targeting with your claims.
Standard fare of patent pool operators, and it's high time to reciprocate.