I sell some parts on Shapeways. It's a hobby. I get a couple bucks per part and SW gets the rest. I've considered starting my own website, but let's add up the work I'd have to do and $$ I'd spend for those couple bucks:
1. Research, compiling measurements, finding blueprints, taking reference photos, and planning the modeling project.
2. 3D modeling the part, reviewing the 3D mesh to ensure it is printable
3. Applying supports to the 3D model and slicing/exporting it.
4. Reviewing the sliced file and repairing "islands" that won't print properly. Possibly back to step 2 or 3 at this point.
5. Test printing, cleaning, and curing the part. (And printer cleanup, and re-levelling the print head). Possible return to steps 2-4 at this point.
6. Batch printing and curing.
7. Quality control, cleanup, labeling and sorting.
8. Website updates, social media posts, promo image creation
9. Listing product and adding images.
10. Answering queries from customers, managing orders
11. Packing, labeling and shipping packages.
12. Dealing with returns, broken items, lost packages, etc etc.
Overhead: 3D printer, resin, spare print heads and vats, filters, cleaning medium (water or IPA), air circulation equipment, safety gear), possible replacement screens. Packing materials and other consumables would have to be factored in. And I'd have to pay for web hosting, of course.
Needless to say, this is sounding like a full-time business that would require volume sales to be sustainable. I'd have to sell a ton of parts and focus only on products that would sell in large numbers.
Or...I can let Shapeways take care of all of that, and spend my time doing the design part, which is what I enjoy.
If I want to buy a Muncie, Mr. Texas3D's offering sounds like the deal of the freakin' century :D