I'm not seeing this as a viable business idea. Say someone buys a cheap little printer and wants it upgraded so they can print full-sized furniture. How's that going to work? What would be left of the original machine, and why would it be worth using that stuff? How would you be able to keep all the parts on hand to deal with all the different designs of printer there are? Many smaller printers are enclosed in boxes - do you plan to disassemble them, build a bigger box, put all their components back into it and somehow charge less than a factory in China that makes bigger printers in the first place? Where are you doing this, where skilled labor is so cheap?