Unless you exceed a certain profit you DO NOT have to file taxes. However with the card business you can almost certainly make a case that you NEVER make a profit. Using card prices and card sell values to your advantage as well as inventory against your sells profits you can turn your $10,000 profit into a $4,000 loss.
Please note im not telling you to cheat the system, just letting you know the card business is pretty fickle to file taxes yearly unless you actually own a brick and mortar or run a business online full time.