The IT department can't maintain it themselves, because they didn't write the program and don't have the source code. So at least some of the support has to be

The IT department can't maintain it themselves, because they didn't write the program and don't have the source code. So at least some of the support has to be from the vendor. Some customers will have competent admins, who like to solve problems themselves, they probably won't be a huge issue (except for the ones who do crazy and insane things). Other customers won't, and you'll get contacted all the time.