Some industries have standardized affiliate marketing which you don't have to think about. For example booking.com for hotels or Amazon for retail. They take a percentage of each sale they make for you and that's it. You don't pay them anything except for confirmed sales.

If you chose black hole paid advertising, then at a minimum you should give out different voucher codes on each channel you advertise on, which give customers a 10 or 15% discount. And give voucher codes to friends, family, colleagues and contacts that they can give to anybody they like. That's the only way to find out where the real customers are and where to target your ads.