Getting assembled is always cheaper and more customizable for the end-user. Regarding trust for non-IT aware people -- they have to be convinced showing them the price - performance ratio. The buyer has to convince his parents that he will take the onus of warranty and maintenance of the system. For the amount spent on a branded system the buyer can a) Get a much better system for the same amount, or b) Save a decent amount of expenditure.
Even if it is a non-gaming rig (read email/web/MS-Office) the assembled part cohort will be far more ideal and optimized for the job. Plus forums like TDF are always here, where experts can advice (forum/email/phone) and keep the rig well oiled and running. It is just a myth which the branded computer lobby has created that assembled is inferior and/or more headache(s) in terms of procurement and after sales service.
Go for assembled, even if it means a few small arguments with elders...! They will understand end-of-the-day.
