I always ask my potential peers how they feel. Are you stressed, relaxed, happy, sad, mad, excited, ambivalent. What works great, what needs improvement. Ask them directly: are you happy with your scrum/agile process? Be careful though as just the words might trigger some ;) If they won't let you talk to your peers and instead you only get to talk to the manager and team lead, be wary: they might be trying to escape & say anything to hire new people. And if they say they are very very excited to have you on board, I'd say that's worrying too, unless you are some kinda rockstar. Also check out Glassdoor and other review sites.