Lost a job interview because of that!
I used to be involved with the forefront of networking using my systems as test beds to make sure that when something new came along it worked for us.
When ISDN routers became a thing, it was obvious from the get go that they would connect as desired then drop the link when idle.
As the Connect Charge was higher than the usage charge, it was possible to easily make multiple calls in the short period of a "usage time unit" really tacking the bills. so I worked out immediately how to configure the device to keep the charges to a minimum.
I was trying for a job in a major local employer with international stores, who wanted a new network man.
As per usual, the job had been specced by someone who knew little about networks so the proposed content and context were a bit iffy.
As I was leaving a fairly secure position, I was concerned about where the job would "go" as the proposed function would not take the year plus they had allowed, but could be easily accomplished over a weekend, or maybe a week at the outside, which I pointed out when querying the role prospects.
I asked them what equipment they currently had and as soon as they mentioned the new routers they had, I told them they had to reconfigure them from the defaults before they used them or they would run up large bills.
They looked at each other and ended the interview. Apparently they had these strange large phone bills they could not account for and having had the cause revealed, they assumed I had been fed inside information by their previous network consultants in an attempt for them to get back into the company good books, thus ruling me out.
The good part was they hired a paper expert from "London" who took a year to do the job with an expensive solution and got it so wrong they parted company at that point.