The Jaguar is not the N64 with regards the amount of bootleg copies out there. Loads of rarer N64 titles have popped up on your AliBaba type stores, and then you can buy a reproduction box too and manual and try selling the game on, but that has been happening for ages now. It's really been the N64 and Megadrive that have seen all their valuable collectable games copied to death, on the Jaguar it's not worth the hassle as (has already been stated on here) Battlesphere is the one copy that will turn up but people selling it will always be listing as reproduction. No one seems to be selling copies of Another World which would seem to be the only other one worth bothering with on cartridge (don't know if that's on a bigger memory size cartrdige than the norm).
On Jaguar there's not enough profit to be made from someone selling copied/bootleg games as the user base is so low compared to Nintendo and Sega machines. The N64 really does appear to be getting clobbered with copies and bootlegs, and I can see why - vintage games are big business, and some titles are worth a fortune so people will always flood the market with them for as long as they can - that's the joy of the Jaguar in a way, if you collect for that then the games are going to legit - sealed games (as stated) have the tag inside them, and nearly all of them sealed games range from $20 (Checkered Flag, Dragon etc) to $100 (Raiden, Defender 2000) and then a bit higher for Alien vs Predator, then higher for Another World, then much much higher for Battlesphere, but one thing you will be getting if you collect for the Jaguar is the original game.
The real pirates out there are making their money on the more popular consoles, and the rarer games on those - collecting for the jaguar is a solid bet that what you are buying is legit. Just steer clear of Battlesphere's in the $100 - $200 price range.
It really is a great machine to collect for and a machine that a full collection of used or sealed games is achievable to collect without breaking the bank unlike collecting for some other machines where you will need to remortgage the house and then keep your fingers crossed that the games are legit. I just wonder who out there is trying to replicate the Nintendo plastic seals and then they can seal any old rubbish into a reproduction box and sell it for a fortune knowing that the seal will never be taken off the box, so the contents of the box will never be fully checked.
In my opinion, the Jaguar is a very very safe bet that what you are buying (sealed or not) will always be legit - there's just not enough money to be made by pirating Jaguar games.