Fanzz for 12 years, and we always had a decent BYU section.
We were the furthest south store in the valley, and Utah fans bought their gear at a 5:1 ratio compared to us.
We had an unwritten rule for selling to each fanbase:
Utes: Upsell and try and get a jersey, and anything else
Cougs: Just give them their t-shirt, you're wasting your time trying to get them anything else.