I know that there's the mass production, and things no longer being made, but the problem is that a lot of those games are certainly not rare, and do not warrant the prices these people are attaching to them.
The main problem is that retro games are "in" right now, but only NES and up. There's no 20/30$ Colecovision carts, for example, despite a lot of them being much more rare than random copies of bad NES games.
Fellow Montrealer here. Personally I gave up on buying retro games in stores in stores and flea markets, they're all absurdly overpriced, from my experience there are only two types of sellers around here:
1) The clueless seller: Has no idea what he's doing and just sells everything at a crazy high base price for crap nobody wants, and then doubles that base price for games that are well known/beloved (regardless of whether it's rare or not, again he's an idiot who wouldn't know).
2) The scummy seller: Actually knows the current asking price for games on eBay, but sells everything at [eBay price + $10-15], meaning there's literally no point in going to his store because you already know you'll get everything cheaper on eBay (which is already not a great price to begin with).
So, yeah... just not worth bothering. It makes me sad because these assholes will probably keep these games forever (since nobody will buy them at those prices) until they throw them away because they need more space or are getting out of that business.