"Working the upgrade" at Hertz locations in Europe
I've become pretty good at working the counter staff at US Hertz locations to get a good upgrade by pitching in some extra $$ and allowing them to try to upsell me. Often a good upgrade can be had for relatively low $$.
However, in Europe I have not been able to work any specials at the time of rental. The counter staff there are able to put me into a different category of car, but then want to reprice it as if I had booked it into the higher class on Hertz.com -- in other words, no real deal.
Any tips to get a better car in Europe? If it matters, usually I book an I6 class and get a BMW 3 series.