Dollar in mia
 

Have booked 4 door Compact car with free upgrade to Intermediate 4 door at MIA.
Am picking up about 10.30 am on Saturday 14th November; shouldn't be a busy time.

Does Dollar still keep the Chrysler Sebring at MIA as its 4 door intermediate car?
They also used to keep a PC Cruiser which I didn't like much but I haven't used them for a few years.
Do they allow you to choose your car like Alamo do?
Car hire company said Dollar are bound to honour my free upgrade and offer me a car in the Intermediate 4 door range--anyone had experience where a free upgrade that wasn't honoured through lack of availability?

Once at my Hertz HLE. It was 2 years ago, at 5:45 PM right before they close. I booked a compact for the same price as economy with an upgrade coupon to intermediate. The manager planned to give me a Ford Fusion, but the previous renter smoked in it so he had to take it out of service. He looked at the coupon and said, "It says as available." He gave me a compact Cobalt instead.

Sounds like you were unlucky as you turned up just as they were closing and they probably wanted to fob you off so they could get home quickly.

I asked if they could go get an intermediate from Newark Airport. They said they're going there anyway to exchange their out of service (smoked in, and several body-damaged) cars, but in the morning, not after closing time. They said if it were earlier in the day, they might have been willing to do that for me, provided that I was willing to wait several hours.

When I came back the next evening to return the car, all the out of service cars were gone, and parked in their place were several unfamiliar cars. The agent said the manager wasted the whole day driving back and forth an hour each way to the Newark Airport workshop to exchange the cars. The manager nodded, as he was sitting nearby and overheard us. He looked sore and tired from all that repetitive driving.