I don't know if this the same discrepancy. I am UK based Avis preferred via Amex Platinum. I'm currently pricing a rental for a trip to my in-laws in the US. On the same site (avis.com) using the same Avis preferred/Wizard number I get too *very* different rates depending on whether I select country of residence as UK or US.
UK residence gives USD 663.36
US residence gives USD 399.88

For exactly the same rental specification and with no additional insurances selected (as per the benefits with the UK Amex Plat charge card). Is there a good reason for me being charged an extra USD 263.48 for being a Brit? What are the repercussions of selecting US residency?

X.