Another data point. Used a gift certificate at the Hampton Inn Rehoboth Beach with some difficulty. The front desk clerk called the manager to ask how to enter it. He managed to enter it into the system but the gift certificate was not applied to the bill. The manager eventually corrected the bill so the gift certificate was used. No issue using the entire amount.

Of the 3 times I have tried to use a gift certificate, the manager knew exactly what to do in 2 of them. In the 3rd, the manager was clueless in more than the gift certificate.