Ah I see, thanks for clarifying that. Yeah that would make sense, if he did sell ROM's then that would be pretty illegal. So he's just selling the hardware which harbors the ROM's that the consumer has the responsibility of getting. Gotcha.
Wait, you thought that these type of carts are sold with games pre-installed on them?
With the exclusion of certain people selling secondhand carts on eBay, for these types of carts specifically you will have to look for the games yourself, which isn't really as hard as some people might lead you to believe. If your Google-fu is on point, you can find almost any game. That said, selling this type of items with pre-installed games is something that's not exactly allowed, but people get away with it. For instance, since I mentioned eBay, they specifically prohibit this, but you'll find dozens of different listings offering 500-in-1 carts, most of the time for the NDS, which often use R4 knockoffs to achieve this...not to mention most of this listings come from China. But like I said in my last post, it's a gray area; eBay for instance has their rules concerning this, but there are ways to circumvent them, especially when there's so many listings of near the same item and their bots are as competent as a monkey with a wrench. To give you a better example, you can sell an NES Classic on eBay no problem, but you shouldn't sell that same NES Classic with additional games on it, but hey, you'll still see people doing it. The entirety of the mini consoles are a perfect example of this. The website's reliance on their bots and people actually reporting these type of listings is what pretty much causes these listings to stay and permeate the website: the bots don't work as they should and most people just don't care.
Anyway, before I keep going off on a tangent, all in all, as I often tell most people I know that want to get into "retro gaming", I would recommend you to invest in a flash cart. Unless you were fortunate enough to amass a collection before the boom, or happen to have deep pockets and don't mind spending a fortune on games, flash carts are an excellent way to experience and play the games you want...other than your computer and an emulator, of course. You're on the Internet, just a couple key strokes way from learning and finding what you want, so dig around the web, there's plenty of written and video reviews for whatever flash cart you may be interested in. Overall, they're a great investment, whether purists want to admit it or not.