Preview models are often low-poly, untextured, or use watermark shaders. Ripped geometry is typically:

If you are a student, look for educational licenses or free asset packs provided by stores for learning purposes.

However, the war on model ripping is far from over. The ongoing battle between Turbosquid, model rippers, and the 3D art community serves as a reminder of the complexities surrounding intellectual property rights in the digital age.