I'm curious, why couldn't he change the plugs himself?
The back plugs are up under the cowl and damn near impossible to get to.
The plugs go into the top of the head and have problems with dirt getting in and around the plug. If you don't carefully clean the area before removing the plug you stand a chance of getting dirt into the cylinder and or on the threads and can gall or even strip out the threads.
It's an all day affair for me to change the plugs on the 5.4 or 4.6 and it isn't because I'm 61. They are just a bitch to get to.
Brad