swanscn

I do not know that this is unique to Thrifty, I think they all try this from time to time. Here is what I would do, join the loyalty program (if it is free) and always use your number. This way your rental preferences regarding ins and gas are set. Verify your cars conditions before stepping into it. i have even noted what I was told was dirt but looked like scratches to me we disagreed but I noted it anyway. Expect excellent service regardless of your insurance choices, if you do not get excellent service take your business elsewhere. If you think you are getting the short end of the deal, do not accept the car request a different model. In my case Avis knows I will not accept a PT Cruiser HHR or any "Upgrade" to a SUV, or Mini Van. Do not let them bill you for wear and tear items this is part of their cost of doing business not part of your cost for doing business with them. Wear and Tear items include tires they sometimes do go flat, not if you hit a curb and blow out a sidewall that is not normal wear and tear. I have never been charged for a flat tire ever and I usually request they repair the tire or provide a replacement car (they only come with one spare).
In today's business climate if you do not think you are getting the value you paid for, please do take your business elsewhere. This is what I do anything else is just not worth the hassle life is to short.
BTW, if the rental company charges for their frequent renter program go elsewhere (that was for you Hertz).