I saw this in a course for sales agents.

Problem:
The word “back” is redundant in this expression.

Explanation:
The expression was part of advice in a company’s course for its sales agents:

“Once you have determined which of the 4 Ps applies, mirror back (or paraphrase) to the customer what you think the objection is to be sure you are on the right track.”

The word “mirror” means reflect when used as a verb, and the “re” in “reflect” means back.

So one could argue that a “mirror back” action would never reach the intended recipient.

Solution:
“… mirror to the customer …”