I tried to use a gift card at a Residence Inn last summer. It was a nightmare. They could see the $100 balance, but couldn't figure out how to charge it. The manager at one point suggested that I pay with credit card, then mail my $100 gc into Marriott to be applied to the balance.

I agree that Marriott should train their staff how to process their gift cards. How hard would it be to email all their managers step by step instructions for them to tape to the wall? I mean, seriously, this is not Rocket Science here.