If anything seems odd ask questions

Who is coming out to work?
How long have they done this?
Do they get a commission for sales?

Any Tech should be able to explain in
plain language questions they hear
 everyday like.    What is a BTU?
Why do they size ac in tons?
What is the difference in R22 & 410?
What they found wrong with your system
and what it will take to repair it.

This site has a lot of information