A mate of mine worked in the credit control department of a company that did something similar with telephone lines.
He packed in the job eventually. He would be ringing customers looking to talk about unpaid bills, they would tear him a new one quoting all these promises that the salesman made.
The salesmen would basically promise the prospective customer a load of shit that wasn't possible, just to get them to sign on the dotted line.
After that it was up to my mate to pick up the pieces.
He said it was a horrible existence, so he packed it in.