Depending on when we are on road trips we may or may not have a reservation.
We will have a short list. DW will call, usually after 4 or 5PM, tell them we are 1/2 hr away and then ask for their best rate. The clerk knows that they have one shot at this.
More than once we have driven into a place and looked at how many cars were in parking lot. Then we called from outside the hotel/motel to get the best rate.
Never walk in and ask for the rate. Ask for their best rate.
It works.