I'm almost certain that I bought the car you're referring to in this thread!
I was a little hesitant when I saw fleet vehicle history as well but figured I couldn't lose with the Ford certified pre-owned warranty coverage.
One of my previous used cars was a rental before I purchased it and it was very good to me. Of course this may not be true all of the time (certainly hope it is for me though
) but these types of histories do not necessarily mean a vehicle has been thrashed.
Overall I'd like to think they're well maintained (maybe even more so than a car owned by a typical person) because it's in the best interest of the entity holding the vehicle to take care of it in order to protect their asset and get the most for the vehicle when it's time to retire or let it go.
Maybe I am just in a delusional fog though and can't see the forest for the trees but so far everything seems kosher with the vehicle and ther have been no hiccups however, who knows what the future may hold but hopefully, if anything goes horribly wrong due to its fleet vehicle history, it will still be under warranty then and Ford will take care of it.