There is a Report button on every listing. And there are restrictions on "choice" auctions. The seller has to be able to supply any of the items he advertises.
Sounds like this guy has a touch of testosterone poisoning,eh?
Ah well, you and your son have a teaching moment, and good for you for supervising him while shopping on eBay!
I went to the Geek Market here in Ottawa a couple of weeks ago and the Lego Club were displaying their works. Wow! Wowie Wow Wow! These are adult hobbyists and they design and build with Lego, making original designs not from kits. If you and the kid ever have a chance, go see what your local Lego Club are doing. He will be impressed!!