We can't stop you from listing tickets on multiple resale platforms, but do so at your own risk.
If you choose to list your tickets on CashorTrade as well as other sites and you end up selling your tickets somewhere else or no longer have them in your possession, you must delete any listing associated with them from CashorTrade immediately. If you accept a request to buy your ticket on CashorTrade, but it has already sold somewhere else so you cannot complete the sale, it would be considered a 'dropped sale' and you would be responsible for covering the associated fee so the buyer is fully refunded.