Look for Mistakes.

If you collect something, the chances are you know a lot about it. This can be your opportunity to make a mint from a seller’s mistake. They might not realise that they have a rare version of an item, or they might have left off the key information that makes it valuable. If you’re willing to email the seller and ask them a few questions about the item to confirm that it is what you think it is, then you should be able to buy items like these. You can then resell them at a big profit, if that’s what you want to do.