Do you need like some kinda of Glue or oil?
pc techs gain experience and knowledge through thousands of hours of obsessing on their hobby. learn through osmosis. they also have friends and parts bins to test if parts are faulty. you dont, if something arrives doa or goes wrong you will be sorry.
buy a dell
add the video card yourself if you must. that is simple, let dell do 90% of the dirty work and take responsibility for the base system being functional.