Evvvvv :
Why would he pay anyone to do that, I think he should try it himself since new components are quite resilient to static and stuff. Its a fun project and he will feel satisfied when he finishes it. Plus there is a metric ton of tutorials on assembling a PC.
Not everyone enjoys that sort of thing or is comfortable doing it. They may be scared of doing it. They may just want something that works with minimal fuss. Preferring to spend that time doing something else. I have clients of both types. Ones who have no technical skill and want a pro. Those with large disposable incomes and high technical skills. Who'd rather pay someone for a project and do something they enjoy. Rather than blowing a day messing with their IT problems.
While I'm a big DIYer for most stuff. Others would rather pay a pro for IT related work, construction contractors, mechanics, upholsterers, &c. As the op wants pre-built. Why not make them aware of other options in a similar vein they may not have considered or been aware of?