Wow! They're selling a ton of near mint CIB Game Boy games on there.
I've never seen this amount of games in high quality offered anywhere, and the prices seem to be reasonable as well. I can't really tell because I'm not really into sealed retro games but something tells me that people on ebay would be asking maybe twice as much as this guy is.
I also found a dutch website that sells some bootleg Game Boy games through my "research" into Game USA multicarts. It looks pretty neat but I can't vouch for the quality of their store as I haven't bought anything from them.
Still, here's the website if anyone's interested
https://www.flashkaartshop.nl/