When a member joins your community, they're giving you power.
The more people in your community, the more power you have.
That power might mean more money, more prestige, greater efficacy, bargaining rights etc…
Members don't mind you benefitting from their participation - as long as they feel you have their best interests at heart first.
They leave if they feel they're being used.
In fact, they don't even join if they feel it's a marketing ploy.
Trust in almost all institutions is shockingly low. It's hard to overcome this trust gap.
If members don't believe your motives are sincere (often personally you, not your organisation), they don't join or participate.
Read The Guardian's membership announcement. You can now become a member of the Guardian. The article notes readers would happily give the Guardian money to be members.
Does that sound like The Guardian has sincere, honest, motives?
Members might not mind paying but they don't want to feel monetized. They want to feel the Guardian is supporting them to achieve their goals, not vice-versa.
Visit Netropolitan, a homepage so bad it might be a spoof. Do you feel the nameless founder has the best interests of his prospective audience at heart? Do you feel the exclusive, rich, audience they're targeting is going to trust this site?
There are three key elements here:
1) Have a named founder (or founders). It's easier to trust a person than an institution. Ensure your community is founded by a named person who can explain their motivations for starting the community on behalf of their organisation. The more the founder is known, respected, and connected to prospective members before launching the community, the easier it will be.
2) Explain your motives to members. Explain clearly how you benefit from hosting and running the community. Don't be coy here. Be direct about why you're doing this. Don't let members' suspicions run wild. Better yet, explain how you only get what you want from ensuring members get what they want.
3) Ensure your actions match your stated motivations. Prune your own social media posts for any possible action/comment that could expose you as a hypocrite. Always act true to your motivations. Moz's Rand Fishkin is the best example I've seen here. Don't become affiliated within any group that would make it impossible to work with any other group in your sector.
This advice runs contrary to the majority of branded communities. Yet, it's exactly what community shows to work.
Right now, most communities founded by organisations fail. Communities founded by amateurs succeed. We trust the motives of amateurs more. We're willing to help them become successful because they're helping us succeed.
The challenging facing most organisations is to find the right person they can help (and maybe hire) to found their community. If you have an existing community, be clear about who started it and why.