I have a common problem with pilots rding the brakes when they fly with me in a PA31 I manage. I've lost track of the number of times I've had to tell them to stop riding the brakes during taxi. Often they deny they're doing it, but I can feel the deceleration or see the pitching as they steer. When I look at their feet I can them with their heels too close to the pedal, causing them to use their instep on the bar and their toes resting against the brake pedal.
Some just flat out deny they're doing it. One of whom has large feet so it's particularly easy for him to activate the brakes. Wish I had microswitches on the brake pedals coupled to a warning light, horn, or cattle prod attached to their person.