The only affiliates that really want to bid on your brand keywords are coupon sites – Slickdeals, Couponcabin, Retailmenot, etc. because discounts are incredible clickbait, and with the 30 day post-click attribution windows (which most affiliates are set up on), discount ads on brand terms work out to be very lucrative for affiliates. So brand terms are usually out of the question.
The question does come up in regards to “brand + coupon” keywords though. If customers are proactively searching for coupons it can make sense to let affiliates bid on those keywords. The cost is all incurred by them, you only pay if a sale happens and if you were to put an ad up for your site like you would for a typical brand term, customers would likely bounce because they want to find coupons, not your homepage.
Some brands don’t want a coupon page on their site because they don’t want their products associated with discounts, but If you do have a page on your site that feature coupons like this Macy’s page, not letting affiliates bid on your brand + coupon keywords so you can have all that traffic for yourself can be very effective. The problem is this: most visitors don’t believe the brand’s page will have all of the coupons that are really out there. Chances are they will click on your ad and then leave to a coupon site anyway to see if there are any more coupons out there.
I think there are three options:
Because of the 30 day attribution window in search, most of the “brand + coupon” keywords are not last touch (affiliate is) but are still taking credit, so the paid search marketer loves the coupon keywords in his account because they perform really well and pull up account performance overall. Parting with them would mean doing what is best for the company, not whats best for his channel.