Unless you know about aircon, you will most like kena cheated by
the technicians.
Once you call them there will always be problems real and
invented.
If your aircon has all the gas in there, and they say there is
no gas, and need top up, what can you do? You say no, they sabo you
and leave you aircon faulty. You top up, you are doing the
unnecessary.
You are at their mercy.