First of all, it's against fire code. CMs are asked to report any suspicious rooms with air mattresses as it is an unsafe practise. I know this because the hotel manager was saying this over and over to the family being removed. It was during March break 2010 and no other rooms were available.
People do know and people do care. There may be on or two rooms that attempt this a night per hotel, not hundreds as you suggest, but if detected they will be asked to pay for a second room if available or be asked to leave.
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