Actually custom build PCs can be the best value per performance is because we actually buy the best price per performance(among all shops) parts and build ourselves.

It is not really a good value if you buy custom-built PCs as they tend to mark up the price a little, keep the extra cables/freebies for themselves and resell them, or selling near obsolete or low performance models and/or parts to you guys. (Not all shops though but 99%)

Just two cents from a guy who have built more than 20 PCs.