Is letting the user know how much they are paying a bad practice?

1. What should you avoid doing to prevent user errors?
2. What is heuristic principles?
3. Why is it not proper for a computer to blame user when error happens?

What should you avoid doing to prevent user errors?

Prevent mistakes by helping the user to build a good mental model of your interface. Use design patterns that communicate how they work to users, encourage users to double-check their work (especially before deleting), and warn before mistakes are made.

What is heuristic principles?

A heuristic is a fast and practical way to solve problems or make decisions. In user experience (UX) design, professional evaluators use heuristic evaluation to systematically determine a design's/product's usability. As experts, they go through a checklist of criteria to find flaws which design teams overlooked.

Why is it not proper for a computer to blame user when error happens?

The term “user error” implies that the user is at fault for having done something wrong. Not so. The designer is at fault for making it too easy for the user to commit the error. Therefore, the solution to user errors is not to scold users, to ask them to try harder, or to give them more extensive training.