Way too many variables to give you a solid answer.
In general, copyright laws cover the "Look and feel" part of something. Taking a design and using it definitely violates that. Can you change it some, and the use it? there you get into how much does it look and feel like the original. Thats where courts can take a wide latitude, and lawyers make a lot of money.
If it is a design that is in the public domain, then you need to look at the rules of where the design was hosted. Most likely they say you cannot make money off their designs. Can you change it and call it your own design? How many stickers and dents do you have to put on a ford rancharo before you can call it a chevy suburban? No matter how much you change it, you cannot change the fact that you started with someone elses design.
Can you start from scratch, and make a similar design, and call it your own? thats where you get back to that look and feel aspect.
Whats the chance of getting caught on facebook? depends on how wide and far it is advertised. nobody can give good odds on that.
What would happen if you are caught? Depends on where the design came from, and who originally designed it. it could go as far as a lawsuit, with the looser paying the other sides legal bills. The winner is the lawyers. It used to be sort of safe to say if you have few assets, they will not go after you, but not any more, lawyers are going after poor folks, and driving them deeper into poordoom, And most places, legal judgements cannot be erased by bankruptcies.
Can you advertise it as just selling the printing, and not the item? That is splitting hairs, all depends on who owns the design, and how far they want to go.
I would not risk it.
All of that is why right now the lawyers are saying we cannot allow members to sell things that have been printed out. Will they change in the future? We will see.
Also, I am not a lawyer, not have I studied these issues to any extent. Also laws vary widely by by state, country, and many other things that have not been thought of but will become issues down the road due to the internet, and these posts going globally.
