In all fairness to the salesperson, they're probably required to maintain a quota of extended warranty sales. I know when I was working retail at Sears, we had to have at least 8% of our gross receipts in warranty sales. That wasn't 8% of sales, that's 8% of the income we generated! If we didn't hit our target, we had to come in at 7:00 AM on Saturdays for a weekly PA meeting, our hours would get severely cut if it happened more than two pay periods in a row (like from 50-60 hours on the floor to maybe 10 hours on the floor, death for a commissioned salesperson), and if it happened for a few months, you were probably going to get fired.
The sad thing was they also kept cutting the commission rates on the actual merchandise and kept boosting it on the warranties to give us extra "incentive" (read: you can't make a living otherwise) to sell the PAs. They did this especially on the good stuff that never broke. Normally, we'd sell the good stuff so that we wouldn't have to worry about losing the commission when the crappy stuff came back, but if you're forced to sell the crappy stuff just to hit your PA percentage and make a living, it makes you do some stuff you'd rather not do.
Now say what you will about the choice of working commission, but some people are damn good at it. You can make a good living with it, but with the advent of every store pushing extended warranties, the honest salesperson is going to disappear and you're going to see a lot more lizards in there trying to foist the stuff how ever they can.