Omg this is exactly what I've been doing too, spent a mini fortune haha! I've got some bargains off eBay buy games like Streets of Rage 2 still command a high price.
Some good games on that list to inspire me!
Do the CEX games come with manuals? It doesn't say on their site, only if boxed.
There's no way to know. Some came with manuals and some didn't unfortunately.
Searching on eBay has become a bit annoying though. Basically having to look for games that look in worse condition so you arent worried that you are getting a repro cart! Worse for SNES I think as a lot of Mega Drive repros look off but still annoying.