Like any other service I would use, I would expect nothing less than professionalism from my plumbing service. They are a very important company when it comes to keeping the plumbing in working order, so should something happen, they need to conduct themselves like professionals.
I'm like other people where I may get irritated with a plumbing incident. They should understand that and not be rude or have an attitude when they arrive. I know they should treat you with respect and get to work right away to find and correct the issue.
The main focus of a professional company should be to help you. These types of issues can be alarming and sometimes scary, which is something they should understand. They should do all that they can to get your plumbing back on track, while also handling themself in a professional and polite manner.