It's probably curbstoning. The guy is an unlicensed dealer, and is selling cars without transferring the title to himself first. If he sold them in a legit manner, he would be on the hook for any state required warranties and any false statements, which would be fraud.
With no paper trail to him, you would have no real recourse.
Ive run into this as well.
My neighbor buys and sells cars for a living, but after selling a bunch with his name on the title, the state came back and told him to get a dealers license.
(he would buy, have seller sign over to him, then he would sign the title when he sold it)
So now he buys the car, has the seller sign it, but he doesnt sign it when he sells it, so to the state, it looks like the original seller sold it to the current buyer, he isnt the 'middleman' or 'dealer'