Let me tell you a bit of what you would be "in for".
Many of these knives need a screw or two. Maybe half. You would need to figure out the size and screw and be able to replace it AND charge fairly for your time. This means you would need to gather up a large assortment of screw types and sizes.
Other knives are just flat worn out and would require you to fabricate back springs, blades, etc.
Other knives have the scales chipped, cracked, etc and need to be replaced.
Many times these knives retail for $50 or less so you can imagine how much someone would pay. Many times these are family hand me downs and money isn't all that important.
Taking apart and rebuilding a folder, especially a soldered folder or other slip joint design is not all that easy.
A fixed blade rehab is a bit more straight forward and you would just need to work out the details with the customer.
In a week or so, I will gather up names/emails/phone numbers of those interested and I will email this out to people that contact my supply business for parts or repair.