You can add limits, we have something like that in Poland, if you sell more than SOME_AMOUNT_OF_MONEY in a year in used goods, you’re considered a business and have to pay income taxes. There are also tax procedures that determine if something was bought to be used and then sold after some time or someone basically is buying stuff from retail just to sell at higher prices. You can also clamp resell value in such cases. Possibilities are limited only by our imagination and throughput of tax controllers.