Paying Upfront

Hello AMP enjoyers,

How often do you pay upfront? I would prefer to pay the tip at the end, depending on how much goes down. At the same time, I can understand that providers don't want to perform a service and then end up with less than they imagined.

Asking this question for either a scenario where you're going in and the provider tells you options, or where you're going in and the provider knows you're coming in for HE+ but doesn't go over options explicitly