I had a poor experience with Avis when I collected as LAS and the nice chap told me I had been upgraded to a far nicer car... when returned to SJC there was $300 extra to pay for the premium car. I refused to close out the rental and after a lot of frantic phone calls, they reluctantly took my word that I did not opt for the upgrade. Annoying thing is of course my signature was on the documents as you sign the electronic screen not paying attention to much after the long flight..