I hope you didn't pay that shop much, if anything. Do you mean they hooked up guages to your system and using coinciding ambient air temps, did not verify that it was correct? How long did the car run, in a/c mode, before they took the readings?
Actually, your system may be overcharged, if their readings are, in fact, correct. The Haynes manual on auto-airconditiong quotes 22/low/suction and 265/high/discharge at ambient air temp of 80F. What was the ambient air temp? (measured 2 in. in front of the condensor) Even then, outside air temp would be off the scale (100F++) for that pressure reading on the low side.
How much do you trust their readings?
Actually you are local to one of the trusted sites mentioned by some of the air-conditioning veterans that frequent this forum. Try
www.ackits.com they are located in Phoenix. They also have a forum strictly for automotive air conditioning.