Dealer is only one touching my AMG. Tires might be a little higher but they know what the pressure should be and won't destroy very expensive wheels.
Wal Mart has changed oil in my pickup and would not listen to me on what air pressure should be. Different tires from original. They insisted they had to go by the sticker on door. Michelins run at much higher pressure. Rear end skidded off the road on curve because tires were way too underinflated.
Many shops seem to think they have the right to destroy your rims and did so on f150. They set a tolerance on balance too, apparently. Close is good enough for them.
As far as gauges I have a bunch of them. Paid quite a bit for each of them. Not one agrees with the other and none agree with the gauge on the pump plus they refuse to seal to the valve stem and give a good reading.
So I let the Dealer do it. They seem to get it right every time.