your statement is one reason I get piece of mind doing my own work if possible. I am in control of of doing the job properly or not...not hurry up cause it's Friday' etc. and skip the valve check or use the old gasket and spark plugs, etc. And charge the customer the full price and 6 mos down the road you wonder why you have a burned valve. Not saying this happens.. but
Also, there is always that risk of an error or mistake on my part that can get very costly...with piece of mind, I sleep better!