For a $100 stereo, no.
For a $50,000 car, well, thats when things start to get real tricky.
Are they currently going to Mexico to get that $50K car for the much lower Mexican price? And when they bring it back into America and REGISTER it, they are going to get taxed. Trust me.
If you don't believe me, ask anyone who bought a new car in a state they don't live in if they had to pay the tax as if they bought it in their home state when they registered it.