Vanmar sells Michelin's, the rider may be sponsored by Vanmar, Michelin or both. The same thing applies with all the tire vendors, they are Vendors of a product and choose who they sponsor. The Vendor sells a product the same way as any shop, they have over-head and need to make a profit to remain in business.

Now if a vendor was selling above the retail price yeah that is BS to me. I told everyone to buy Pirelli's when I raced for them, street tire or race tire and if I was sponsored by Oscar and 303 Cycle I would tell them (street riders) to buy Dunlops from Oscar if they were up north or at the track, and 303 if down in the Denver area, but that's just me.

Like Jim said, a racer's sponsorship level is between them and the vendor/supplier/shop/manufacturer and shouldnt be public knowledge. I have been paid to use a product as well as receiving that product for free, it was never common knowledge how much or even if I was paid as far as I was concerned, my job was to wear and promote their product as per our contract