Ah yes excellent Rukya, otherwise, here is my method:
1° In room I choose a masturbation pose, I asked him to ejaculate...
2° I wait ...
3° If he says: "I can't" I replied: "Go see a doctor"
And here I have unmasked a false premium
PS: Also works for girls
Just kidding, a lot of free users spend premium precisely because they can't ejaculate. this is their primary concern