MacStories has a follow-up to a Wired report that details the practice of selling access to Apple beta software. The Wired article profiles several websites that'll add your UDID to a developer account so you can download and activate iOS betas on your device. Each site charges a small fee, usually under US$10, for this service.
According to the MacStories report, Apple responded to this Wired report by sending DMCA notices to these sites and their hosting providers. As a result, sites like activatemyios.com and iosudidregistrations.com are being shut down one by one. You can read more about this take down, including the response of one website owner, in the MacStories article. As of the writing of this post, there is no indication that Apple is targeting users who have purchased an activation.
Apple iPhone 6s