We have a steady stream of projects here where someone has a broken or missing doo dad they need a replacement for, and replacements are made of unobtanium. Recent examples include:

Replacement marker light lens for a car
Replacement part for a chair
Replacement part for a camper window frame
Replacement paddle for a breadmaker
Replica glovebox door handle for a 1974 FJ55
Replica "Turbo" grill badge for a BJ74 Land Cruiser

The latter two has resulted in sales of many dozens to the original customer who then re-sold them to others who had the same need. Most of the structural parts we make with Taulman nylon for its strength.

We also make custom orthotic inserts for a local Pedorthist - he scans the patient's foot, pulls the scan into his software, makes corrections for the patient's gait, then we build him the insert out of Taulman nylon. This bypasses many labor steps in the tradition way to make orthotic inserts and saves the Pedorthist a ton of labor and mess.

I could go on, but the majority of our business is making useful things for people. Most of the time they pay us to design them because they don't know how to do 3D design, and they pay us to build them because they can't justify a printer for a couple hundred dollars worth of stuff. And the ones that go over a certain threshold then buy their 3D printer from us.