There is! You can see it on the main www.squareup.com page.
Here's what it says:
Let’s talk about a custom rate.
We can create custom pricing packages for some businesses that process more than $250K in card sales and have an average ticket size over $15. If that's you, get in touch—we'll even review your current statement with you. An average ticket size under $15 is unlikely to qualify for a custom rate.
