Work done at dealership

I told the dealership that the rear inner tire needed checked I have to lay down and run the house through the hole to get to it.I have a air compresser and had no problem just the one rear tire. I asked them to check just the one tire and the service manger said no problem we will just check them all for you if you want.So I said ok. I store the coach for 6 months under the grand stand for the winter and put 100 pounds of air prussure in the tires . By spring they are down around 94 to 96 pounds .Ever year I let out the extra air . Winnebago sticker by the drivers side says 90 pounds . So they where not adding air they where letting air out.I asked to check the one tire they did all 6 tires. The teck said they where way high and it took him 1/2 a hr to let air out .With a small screw driver it might take me 10 min. In all my years I have never been charged to check the air in the tires. I had a recall from Ford and asked them if they could air down my tires and they said no problem and was not charged.If they do this to me just think about the real old members they play games with .They emailed me back and want the 52.50 for letting the air out and I will have to pay it. I guess you live and learn.They are the only Winnebago dealer close by we live in small town so they are the only option if you need repairs. In the 6 years I have worked on this 2011 I have done all the work my self oil changes lube jobs and Gen set. But now it is a different story with my battle with Cancer.