if another person sell a game made with the engine, he must paid the license in the same way.
And that person not have right for sell (he must subscribe and do the license agreement), easy get it a legal trouble (that person), inclusive if he not make money, they can sue you. You must register and download the engine legally.
if they detect a game sale without knownledge, they can ask you for ledgers and you must show, (its on license agreement).
Its easy, anyway i suppose you must make a good relevant game, they not going to sue for sell 30 copies (that perhaps its the 3000$ per quarter exception)