To be fair, I was told that I would get a f&b credit at check-in, so they weren't trying to do anything shady.
Never attribute to malice that which can be adequately explained by incompetence.
The latter surely true given that I'm yet to see anyone be able to check-out of these hotels with the credit correctly applied or without incorrect advice being given.
The fact that you were told you can only use the credit at breakfast is complete nonsense and should be reported to Hilton corporate.