Avis - One Way Rentals and Mileage

Are one way rentals always not unlimited? I've received conflicting information when I called Avis. The last time that I did a one way I was charged per mile. But I did a one way once recently and they didn't charge me per mile. Is there a way to tell from the app or the website? I've found the estimate tool to be wonky with these mileage calculations.

Also, last year I rented overseas round trip and was still charged per mile. I was told by the agent that this is because I was using a corporate account. Normally it's unlimited. I wonder if this is something that's just try with overseas rentals with Avis.