maybe you should ask him what exactly he means with "confidence" ? In the end, you should be able to get a bet on it. If it fixes the problem, without unwanted

maybe you should ask him what exactly he means with "confidence" ? In the end, you should be able to get a bet on it. If it fixes the problem, without unwanted side effects, you get X. If it doesn't, you pay Y. See if you can work out X and Y. If he really insists on 100%, and wants to pay for it, you might get rich in the process.