picked up my FFAR at SFO.
I asked the guy about "any ideas why i could'nt choose online a FFAR or other selected class of vehicles", followed by "where do u get the cars from if a customer pre-pays a select class of vehicle"

The guy said the SFO will hold a lot of stock anyway, but in some scenario's, they take from other Hertz locations across the city, and vice versa when customers book through 3rd parties rather than direct, due to the obligations they have, etc.... (he said some 3rd party brokers have deals with Hertz, so hertz have to try and fulfil, by utilising airport locations and HLE's, or by not making those class types available directly if 3rd parties have booked out, etc).
He also said "but in the past few weeks, they've seen some angry customers, due to class or specific vehicles booked, and only having mid or fullsize Cars available,. or mid-size SUV's! " !