What's your experiences with revenue sharing

I wonder how does revenue sharing work for something like an Shop, which is provided as SaaS.

I've seen some plans, where SaaS Providers charge the customers via revenue sharing (let's say 2.5%).

Let's say you have something like an Onlineshop. The easiest step is to check the succeeded payments via Payment-Gateway.
But what is if customers purchase on account, or per cash on delivery.
What if customers exchange goods?

Looking forward for your Ideas and experiences for that.