We noticed we were paying repair insurance on our phone lines through our phone bill every month, so I stopped it after about 2 years. Then 30 years later, we had a problem. The service representative was rather stern with me when pointing out that if the problem was in the home, we would have to pay for the service call, but if we had been paying this free repair item it would be no charge. I pointed out how long ago we had stopped the fee and that we never had a problem. so paying for the service call would still be money ahead. I simply said, "You do the math." His answer was, "Oh." ( I do realize that if we had, for example, a mouse probem, the fee would have been worth it.)
A few weeks ago, the heater in the house stopped working so DF called a repair company. The rep got there early and since I was still at my house 25 minutes away, when I arrived at the house, rather than get there before the rep arrived, I got there just as the rep was doing paperwork with DF.
I walked into the house, and DF says, "I'm signing us up for a maintenance agreement that'll be $XX.XX every month, and it can be canceled at any time so it's not a contract." Service guy (notice the change in words) "confirms," "Yes, the service agreement can be CHANGED at any time and, with this service agreement, you get two air vent cleanings 'free' twice a year and a XX% discount on repairs when your heater gives out, which it will be 'cause it's so old and dirty."

Red flags immediately went off in my head since I'd heard about scams when I lived in SD from someone whose elderly mother was talked into paying $XXX to have her vents cleaned when they didn't need to be (and weren't). I looked at DF and said, "We need to discuss it first."
DF's face fell, and the rep offered, "I could go outside while you discuss it." I said no and asked if we could fax the agreement to them should we change our minds. The rep (I really was amazed he said this) then said, "No, if you fax it, then it just creates additional work for HR." (how HR was involved in this is beyond me so I figured he was a dumb-bunny who was pulling tales out of his butt -- anything to make the sale). He also went through this whole spiel about how to return to pick up the agreement would cost the company extra money so it was in THEIR best interest for us to sign the agreement right then (again, couldn't believe someone trying to sell us something would think I would care that THEY would be "inconvenienced" to have to close the sale).
I stood my ground and, as soon as the rep left, asked DF to call his brother (who would know whether or not a maintenance agreement would be necessary). I explained to DF that that is why I wanted to wait; I simply wanted him to check with FBIL and get his expert opinion.
FBIL said it wouldn't be a bad idea so DF called the service guy immediately and said we'd sign the agreement. Fortunately (for us), the guy wasn't interested in coming back and said to go ahead and mail it in. Well, upon closer reading of this agreement, I discovered that this was a CONTRACT and that there was a penalty for terminating earlier than one year (I pointed out that while DF said "cancel," the service guy said "change" -- he KNEW it was a contract and deliberately didn't correct DF's notion that there was no time commitment). I'd also pointed out that those cleanings wouldn't be "free" as we would be paying for them every month. I pointed out a lot of things wrong with the whole mess. DF realized the next day that I was right and thanked me for not letting him proceed with the agreement.
The service guy really screwed his company out of future business because we'll never go back to them.