Submitting designs & ideas for college team apparel

I am a freelance graphic designer who's come up with several designs that I think would be popular among fans of the big universities in my area. I have no desire to produce and sell the shirts myself -- I'd only like to sell the designs, and I understand I need to submit them to a NCAA licensed vendor (there are several where I live, but I don't have experience or personal contacts with any of them).

My questions:

1. After the vendor sees my designs, what's to stop him from stealing my ideas and keeping the profits for himself?
2. What is a fair arrangement to negotiate with the vendor? A flat price? A percentage? How do I keep from getting screwed?

Source: http://www.t-shirtforums.com/general-t-shirt-selling-discussion/t174634.html

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