Let's say I write on my site "If you buy any ClickBank product using my affiliate links, you'll receive bonus x". How do I know if they bought through my affiliate links? I saw somewhere "send me your receipt and I'll send you the gifts". Is my affiliate link printed on their receipt? I know they can ask ClickBank for a refund, but I'll let keep the bonus anyway. It's a risk I'm going to take.
Make sure it isn't an elite super spectacular bonus that will make you cry if you gave it out for free. I suppose you could tell them to email you from the email they purchased with.
Tell them to tell you the name listed on the Credit Card With which they made the purchase or the receipt, and just check your CB account if the user has purchased the product.
Just for your information: You can't since it's again the TOS of ClickBank. If you do and another affiliate see it and report you, you may lose the money earned so far.
Thank you. That's good to know. Now I understand why the opt-in lists owners send me the offer with incentives only by eMail and don't mention anything on their sites.