What may playtesters of my games do or not do? Are there secrecy rules? Expectations that they’ll keep mum and only talk to me or my assigns? That they won’t talk to third parties or potential competition?
No, it is simpler than that. The game-teach and playtesting rules are simple: you can take and send pictures around freely, you can talk about the game freely – good or bad or ugly or indifferent is all fine – but you can only do those things where I can see/participate (tell me about it), and you can only play the game (at all) either with me or with my approval (so I can observe and respond).
My games are all under Creative Commons licenses, I keep no secrets here, but I mind the conversation.