Not sure where to ask this, so feel free to move it if necessary.
Suppose I want to buy a car from my friend for $8,000. To avoid registration costs, I pay him a measly $500 for the car and $7,500 for helping me brush my dogs (or something else insignificant... you get the idea).
Would this minimize the cost of registration/sales tax? Is there anything that prevents me from doing this (i.e. legally)?