This is also why free room upgrades can happen. If they have 80 standard rooms and 20 premium, they'll probably sell around 85 standards. If they don't sell all 20 premium, they'll upgrade some of the standards and outbook any 'extras'
I have no issues with this - where they take the gamble and then have to give a free upgrade; but why should they be allowed to gamble in a way that they can't fail to win, at the customer's expense?
Never known this happen. If the rooms have all been allocated and they are full, how on earth are they 'finding a room down the back of the couch?' Are they tidying up the broom cupboard and sticking a couple of Z-beds in it?
They probably kick the can down the road. If you're assertive enough and demand they make good your booking, that likely just means that somebody who arrives later will get turned away instead, and they hope that they'll be less assertive and will be able to be fobbed off.
I don't get the people who are suggesting that, as long as TL find you somewhere to stay, you've got what you've paid for and have no reason to complain. What if you pre-paid for a meal at a posh, expensive restaurant and then, when you turned up, they'd run out of all of the choice desirable foods, but they could bring you as much beans on toast as you could eat? Would that make it OK, as you went there to eat and you've left full up?