I'm not really sure, maybe if he has all the evidences that he can afford his trip and accommodation here like credit cards with enough money, pocket money where he would stay here, round trip ticket, no objection letter from his work stating that his boss approved of his trip and he'll be back after 2 weeks, or if he has his own business, maybe have a copy of his DTI permit. He'll be questioned about his work. Also have your invitation letter. If it is not his first time, maybe he wouldn't be really questioned that much because as far as I know, they are really strict with first-timer women. I'm not just sure with women.