Go look at your car tires, look at what the max psi is rated on the tire for, then go look at your driver's door or door jamb for a label that shows the recommended tire pressure, note the difference between the two? That's because the manufacturer took the weight of the car, and maybe the average weight of passengers, and calculated the correct psi due to weight. See where this is going?

If you use a tire pressure calculator you will probably come close to the psi the bike shop put in, see: SILCA Professional Tire Pressure Calculator