I’ve never had pushback. Often the client just doesn’t want to deal with the hassle and need someone to do it for them. Let’s not forget that it is not just a phone call. You have to look at transcripts for first time abatement or other issues. You then have to make sure you have all the information needed to set up the agreement. So it is a bit of work.
The flat rate also covers the other cases that go sideways. Sadly a lot of cases seem to quickly stray from anything close to “streamlined”.