The most common mistake I see in basically everyone who is trying to earn money with 3D printing is making products or offering services for everyone.
In any business to succeed you gotta start with a clear focus for a niche, you are supplying your products for.
Focus. The key is focus. As in anything in life, you can focus on 100 goals at a time and achieve mediocrity. BUT if you get your head in the game and relentlessly try to grow in one niche, your chances of success will skyrocket.
A seller without focus is like a plane without wings.
Be an expert in one niche.
If your toilet is broken, do you want a repairman who kinda knows everything or the best plumber in town?
People will order less from someone that makes and does everything.
Customers prefer to order products from someone who is an expert in making something specific - only cookie cutters, props, busts, Pokemons e.c.
If your craft is great, people will come back for more.
Follow your chosen niche and be a respectable expert in it!
If you want to learn more about earning money with 3D printing, check out our 3D Printing Monetization Academy here
To your sucess!