Interesting. Several issues I see though.
1 why do you care if someone is selling below cost? Id it your cost, dealer cost or what?
2 If they are selling below cost is it a dealer that is doing it or consumer?
3 you sold the product already right? So why do you care?
4 if it is a competitor or for a sponsored vehicle you should be keeping tabs on all equipment sponsored and having them sign a 1 or 2 year agreement like everyone else.
5 what you dont seem to realize is this is a good thing for you. It gets equipment into the hands of people who cant buy it at a higher price. So they end up seeing the quality in it and you might in turn get new sales from them people when they can afford it.
6 it is also simple you tell everyone and on your site no one is authorized to sell your products on the net. If they do the purchaser will not get any warranty. As most already know and expect anyways.
7 if people are advertising items for sale and scamming people so what. You cant control that. The buyer has to be careful themselves. People have been scammed for DD, RF, Pioneer, Eclipse, Clarion, and more. You dont see any of them going on forums.
You have to look at it three ways. As a business, someone who might of bought brand new (store only gives store credit) and needs money badly and of course someone who doesnt make alot of money that would love to have thier hads on some good equipment that can actully get it.
I make decent money but with gas prices and bills going up and my pay staying the same I am starting to not be able to afford alot of what I have in the past. So only way to have a chance is to look for deals where possible.