You are right, they do have what I would call an Emerald Aisle Lite which you can take any car in the area and some of them are higher class cars than you reserved. You are also right they they have the upgrade area where they try to tempt you with an upgraded car for an additional cost per day.
Originally Posted by
drzoidberg
It's not a true Emerald Aisle, more of a strategy for Avis to upsell you into a higher class car.
At National, if you find a higher class car in ES or EA you are welcome to take it without paying an additional per diem. At Hertz/Avis EA copies, they tempt you with higher class vehicles...for a fee.