I stopped attempting to monetize. big issue is having control over your design. the only sane way at the moment is either selling the parts to the customer which is expensive and can be stolen, or only dealing with G-codes, and encoding information into the G-code for customer tracking.
using your printer like shapeways to make money is impossible you would need higher end 3d printers and a farm of them to even think about it. The way i see it shapeways will be out of business in a few years as home 3d technology advances and just like a home computer eventually everyone will have one. print farms are going to phase out for home units. much like main frame computers gave way to desktops.
the money is in the Files that create the item not in selling the physical item. which brings you back to the the problem of control over your product. Right now if you happen to create and sell something that reaches a certain amount of sales somebody will copy your design and sell it for a little cheaper locking you out of the market. people steal free designs regardless of license agreement and sell them on ebay or cults3d or what ever other amazon like service exists and then you might shut one down and another pops up in its place.
this is the STL end of it.
that leads to Gcodes but then you have to deal with the infinite types of machines and filament to get a successful print. then you can still lose control over it which is why if you sell the Gcode you put some tracking information inside the file. like 3d printed serial # buried inside the part that you can see with a Gcode reader/render. that at least will tell you whom leaked the Gcode but you will have to create individual models for sale(still possible) but if popular enough the part can be recreated and then undersold.
that got me into exploring one offs for customers. but then you are responsible for the output and if the customer is unhappy they will simply blame you for a flaw in there design and they expect you to fix it for them.
I got contracted by a company to create a prototype which took about 2 weeks worth of printing however these people had no idea how to create for a printer and everything was injection molded design and i had to sit that modifying everything to make it work. i made no money and honestly wasted my time.I also made trinkets for people, like for a party or a wedding a card with a customized 3d printed item to make it more memorable. deadlines are REALLY hard this way on a small scale operation. if a 15 hour print spread over 3 machines has a problem there is no backup and you might not meet a deadline.
when you have to injection mold something that adds another layer of protection because of the equipment and materials so the design is harder to steal.
eventually i would imagine
there will be a self destructing Gcode or STL file type which the industry will adopt this would run along parallel with the free stls we have today. a printer would take either one but the destructing files would help protect companies and making money.