Is it permissible to exchange a receiver (dish receiver) for a different one by paying the difference in cash?

A receiver is not an item of usury (ribawi item); therefore, it is permissible to exchange it unequally or with deferment. It is also permissible to sell one for two, or to sell one for another with an additional cash payment. However, this transaction becomes forbidden if one or both of the sellers use the device for illicit purposes.