Yeah, I think decent pictures and good feedback (especially if they've sold GBA games in the past) are enough. You can also ask the seller directly if the game is legit or for better pictures. I've bought tons of GBA games off eBay, but only one was bootleg. The seller who sold me the bootleg had good feedback, but he was selling his son's game and didn't know it was bootleg. he also had pictures in his auction, but it wasn't very detailed.