The thing that gets me is nobody talks about how the pump fails after you fix the clog. That sock or whatever was stressing the pump for who knows how long, and the motor windings cook a little every time it tries to push against a blocked hose. So the last guy might have actually saved that customer a callback down the road, just for the wrong reasons. Problem is he never checked the hose, so he got lucky on the diagnosis and unlucky on the bill. My rule is if the pump tests good on a direct power jump and spins free, the clog is your problem, but I'll still warn the customer the pump took a beating and might go in six months. That way when it does fail they aren't mad at me, and if it doesn't, I look like a hero for not selling them a part they didn't need yet.