What does a ski rep do? Usually, they have some job on mountain that keeps them in contact with the "ski pros," i.e. patrol and snowsports. So.....they can be a tune/repair shop guy, a lift ops supervisor (seldom a liftie, if ever), an instructor who seems to have a lot of time (too good for groups, ya know), etc. They are guys who are happy for the free gear.
Most mountains have most or all major brands represented, so in reality they don't do much marketing. If you know what you want, you find the guy who reps them. Tell them what you want, wait a week, and it is yours. But, they really don't go out of their way to "convert" you to their brand or make the sale.
They also are helpful in getting you good prices if you are PSIA/AASI or NSP, but it is usually better to find a shop that hosts "pro nights" and has no problem with pro forms. They know the manufacturer lines better than most reps and can give the same prices, and offer better after-sale service.
I suspect that some manufacturers are trying to wean themselves off the rep system. In every issue of Professional Skier, there are ads inviting you to buy directly from the manufacturer/national distributor with your pro discount, not to mention what you can get from the PSIA website. I don;t think manufacturers really need mountain reps, as long as there are shops willing to honor pro forms and available online options.
As for regional or race reps...they are different. They drive A LOT, ski not much, and work their tails off and usually are good for their brand. These guys are working for a future in the company (or for the resume), not just for free gear. But, most are *good*.
IMO, the best reps you'll see are the wax reps at any XC race/festival. The Swix/Toko/Holmenkol guys would bust a lung to demonstrate their product and prove its merit. I have yet to see a mountain rep for an alpine product work a tenth as much as those guys.