Interesting - my experience has generally been the opposite: at least half the time, the walk-up price is less than the on-line price.

On a few occasions, when the on-line price has been lower than the walk-up price, the front desk staff have suggested, with genuine sincerity, that I try booking the lower price on line. Every single time this has happened, when I tried to book the advertised price on-line, suddenly that price was not available on the website... after going through the first few steps to do the booking, the website price suddenly inflated.

I have found booking.com to be the worst offender in this regard, which I why I prefer to use TripAdvisor to suss out hotel prices. TripAdvisor usually offers several different competing booking agencies to choose from, which means that TripAdvisor themselves have no incentive to low-ball a price.

Having said that, there have been a few occasions where a lower price is offered online, and when I have given the front desk the opportunity to match it (without me doing an on-line booking and the hotel having to pay a 15% commission), the employee at the front desk has been unable to match the price because "that rate isn't in the computer". In other words, the hotel management has not given the front desk clerk the discretion & authority to use common sense. When I encounter that problem, I usually go find a different hotel, not because of price issues, but because I've just seen a huge red flag saying "this place is poorly managed".

Michael