Due to the nature of 3D printing, minor flaws and imperfections can be expected. I print these personally at home, please allow for slight variations.  However, rest assured that I inspect every piece that comes off of my printer. The patterns in the plastic are inherent due to the nature of 3D printing, which involves plastic being deposited in multiple layers. As such extrusion patterns are normal for 3D printed products and are to be expected (see pictures).