Wirelessly posted (BlackBerry: BlackBerry8530/5.0.0.1030 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/417)
"How would Budget react if the customer kept picking up a full-size on this offer every time he drops the previous rental with about 450mi on it?"
It's been reported here on FT that Hertz stopped renting to renters who regularly put on more mileage than what Hertz considered reasonable on unlimited-mileage rates.
I have no idea if Budget would take the same approach to someone who engaged in similar conduct on these rentals, but it would not surprise me.