From Registered Apple Developer Agreement (https://developer.apple.com/programs/terms/registered_apple_developer_20100301.pdf)
6. Confidential Pre-Release Materials License and Restrictions.
If Apple provides you with Pre-Release Materials, then subject to your compliance with the terms and conditions of this Agreement, Apple hereby grants you a nonexclusive, nontransferable, right and license to use the Pre-Release Materials only for the limited purposes set forth in this Section 6; ... and you will not modify, network, rent, lease, transmit, sell, or loan the Pre-Release Materials in whole or in part.
This agreement is dated October 2010, so it's been pretty clear for years (at least) that developers aren't allowed to share beta software with their friends or sell it to random "superfans."