Another thing you have to deal with is avoiding annoying your customers by serving them ads incessantly. If people have already converted, serving them with the same ad means you're losing money on already converted customers. So, what do you do when they have already converted?
Simply use a burn pixel, a small code placed in your post-transaction page. This untags visitors who have already made a purchase or converted. You don't need to tell them to take the same action twice.
Rather than show them what they've bought already, think of up-selling, cross-selling or even offering them referral discounts. How do you do this? Through new ads - burn the previous campaign and enroll them in a fresh one.