How accurate are mover estimates?

Has anyone really done those video surveys for moving? NoBroker asked for details and videos of the items I wanted to move and gave me an estimate based on that. It felt more logical to me than the local guy who just asked "1BHK hai?" and gave me a number but I am wondering how accurate those estimates really are in real life.

Do movers usually stick to the quote if you have already shown them everything beforehand? I am not looking for the cheapest option but I don't want the price to change once everything is already loaded.