3D printing is changing the world, but counterfitting shouldn't be a worry unless the counterfit is better than the original! who would buy a counterfit engine part? and who wants a counterfit toy?
I dunno, my better half has a tendon condition and was showing me a video of a device that stretches the tendons to relieve pain, the device itself is pretty expensive for what it is (an ovoid bar with grips on each end), so I spent all of 4 minutes in Fusion360 designing a near enough exact copy, two hours 3D printing and she had one, I will stick the model on Thingiverse tonight so others can try it.
I actually had counterfeit Ninja Turtle toys as a kid, we used to go to the cattle market on the last Sunday of the month during the car boot sales and I would fill a carrier bag with bootleg toys fresh from some dudes garage for a couple of quid. The paint job was comical at best, but the molding was almost spot on, for £20 he would sell you a set of molds and you could knock out your own figures. Wish I bought one and kept it, would be a fun little keepsake.