If they have problems with 'tailgate resellers', then they need to raise the bar on who they are signing up at SEMA to represent their products. Maybe require them to have a retail site, chassis dynamometer, auditable/proven sales figures for the last 5 years...
Most of the 'pricing guidelines' I've seen comes back to preventing turf (territory) wars between resellers, not defending 'brick and mortar' resellers from 'tailgaters'. There is less and less brick and mortar in the motorsports industry anymore - in fact it could be argued that its far and away an internet sales model. Look at Summit Racing and Jegs, for example.
Forward thinking companies have come up with ingenious ways of preventing turf wars, while providing for a reasonable level of price competition. Check out www.h-d.com and see how they have managed online shopping relative to dealer territories.
Manufacturers that promote their resellers, driving traffic to their doors, showing them how to bundle products and services, etc. while providing warranty support will succeed in the end. H-D is a great example of a mega manufacturer that knows the importance of their dealer channel.