Become the non-expert
Many years ago while visiting an aunt, she announced that she'd got a compute for the kids. She also asked me to show them how it worked as the rentals company (yes, she was dumb enough to rent a computer for home use back when people rented TV's, etc) were pants and didn't show them how it worked. Knowing how this was going to pan out in the long term (lots of phone calls and the expectation that I would drop everything and give them free support), I decided to show them exactly how it works and might have accidentally mentioned to them that they can set a BIOS password too.
As sure as shit, the next time I saw her she moaned that I was crap and she had had to call the rentals company how had fixed it for her after the kids locked themselves out. She never called me though, but did bad mouth me to the entire family. Now considering that I have a very large extended family (over 50 cousins all in close proximity) in the 30 years since then I have received zero calls. Not one. They still think I am crap with computers and I'm more than happy for them to believe that considering how ungrateful most of them are .
Now it might seem like a bit of a bastard thing to have done - lead them up the path to failure - but it didn't cost them any money and it's saved me hours of grief over the years.