There are a lot of differences between production and custom. Economy of scale is a big one. You mess up while making a knife and have to throw away a blade, maybe two blades, maybe a couple of locksides have to be redone... but you can't charge your customer extra due to YOUR mistakes, wasted time and materials. Add that to the fact that people are constantly sending back your previous one-off customs for service. You haven't seen some of these knives for years or even decades but they are a high priority and must be fixed quickly. All this while tons of people are calling/emailing you about all sorts of crap and you are making calls and writing emails to people for materials.
Compare this to a factory operation. CNC machines run several hours a day churning out mostly identical, indistinguishable parts and a guy checks them for tolerances as they emerge. If some aren't precise they are just thrown away and it is an expense that is factored in. Assemblers take tons of identical parts from a bin and fit them together. If your knife needs repair, an identical part from one of those bins is swapped out for your problematic one. There's a person working at that company whose sole job is to take your email and pass it on to a repairs department, who likewise are tasked with only that one job to do.
When you consider that one person does all the communication, all the repairs, all the assembly, all the base manufacturing, all the acquisition of raw materials - it's a wonder that these knives even get made.
This is no excuse for sloppy craftsmanship, but it is something to think about when comparing minuscule fit and finish details in production knives and in custom knives. Keep in mind that there are still many makers who make sure everything is more or less perfect before it leaves their door.
Also keep in mind that there are TONS of examples of production knives that have poor fit and finish; lemons can and do come out of production makers at every price point, from Kershaw to CRK.
