If he is selling a duplicate of Saint's book, then yeah Saint can do something about it. If he is selling modified plans to his own design, and isn't violating any copyright issues, then not much anyone can do. I mean, Project arcade was admittedly just a mass of widely available information from the byoac site. As long as this guy cited his sources, then he would be doing basically the same thing, but without the backing of a publisher.
There are plenty of people on here with unique designs for their cabs. They could publish and sell their plans too, and then provide an index to a directory of sites for mame, and parts suppliers.
Having said that, he shouldn't be advertising how to obtain free romzors on ebay. That should get him shut down. Technically, it is not illegal to point people in the right direction, but it is not the right thing to do. I can't get arrested for telling people there is a crack house at so-and-so address so they can buy crack, but I'm not going to do it because it isn't right.
Anyways, the guy is wrong, but the only people on here that have a right to truly get angry at this guy are the people who are dedicated to original games...no emulators.