My job is stressfull too, but I realized a while back that the customer is not upset with you, they are upset with the situation. I also realized that complaining about it just makes it worse, so I don't complain about it, I smile, move on, and thank the good lord I have a job.
If you don't like your job, look for another one, I am sure somebody out there would love to have your job and be gratefull for it, just remember, if it weren't for broken equipment and unhappy customers, you wouldn't even have a job.