I have occasionally had a problem with specific room type availability. I found out after one experience too many that Delta Hotels' Privilege program guarantees smoking/non-smoking, but not anything else. For some reason, the member profile forces a selection between smoking and non-smoking, and I really don't care which it is. And once half the rooms are automaticall eliminated, the odds of getting your queen/king or double-double preference goes way down.
Since I'm 5'11" and sleep flat on my back and don't like pressing the top of my head against the headboard, a double bed, which is 6', leaves my feet sticking at or off the foot of the bed.
My workaround was to insist that they put a big note on my file indicating that I didn't care about the smoking status, but that if I didn't get a queen-sized bed, I would cancel the reservation, and also tell recommend that my company cancel their contract with the hotel chain. I've had few problems since.