Agreed that the Avis agent was sneaky and unethical. Likely due to pressure from management to upsell and getting paid to do it.
At the same time, before I leave, I always do a 30,000 ft, 10 second look, at my rental agreement to make sure: a) that pre-tax rate is somewhere around what I expect; b) It's in my name; and only if I have time c) Due in time, location, car, etc., is somewhat right.
I've caught things before, probably inadvertent, but I always check (10 seconds at a red light if I'm running late) ... even as a Chairman!!
Hey we're all FTers, so already hopping around with heightened knowledge, not to mention most of us rent dozens of times a year (including the OP) - not doing that 10 second 30kft look at your paperwork, your exposure adds up!
Avis hired an unethical agent that earned a commission on your upsell. However, at the end of the day, only we can protect ourselves... Caveat Emptor.