I can only relate to you the bad experience we had last year. We had reserved two minivans for 10 people last Spring and when we got there they only had compact cars left. They said that customers had kept them out longer than they were supposed to. They had a take it or leave it attitude. We left it, walked over to Avis and got what we needed. And, much to Avis' credit, they didn't gouge us at all. We were travelling with 4 adults, one teenager, two 12 year olds, a 7 year old and two 5 year olds along with two car seats and at least a thousand bags
In addition, part of our 10 day trip included 7 days at Vero. There was just no way we could've made the trip in 4 compact cars. (their solution)
I could have forgiven them if they had tried to accomodate us somehow........like making an arrangement to switch the cars the next day or shuttling us to our hotel that night. I don't think they had any reciprocal agreements with the other car agencies either. When we got home, I tried several times to email them and also sent a letter but never heard a word back.
Even though it was such a bad start to our vacation, and we thought we were in the middle of a Seinfeld episode, it worked out despite L&M. Now, we can laugh about it but at the time........no one was laughing.
My advice would be run..........don't walk.......... away from the deal that looks too good to be true. But, if you want to chance it, make alternate reservations. You can always cancel them if you get what you want.