Airbnb is a service that allows people to open their homes to houseguests.  It’s turned couchsurfing into a high-growth business model that has hoteliers scrambling and investors looking forward to an IPO.

But there’s a challenge for Airbnb:  With people opening their doors to total strangers, how do you keep everyone safe?

A couple years ago, an Airbnb user had their house ransacked by thieves, while another found out the hard way that the guests renting their home were meth heads.

For Airbnb to scale up and succeed, they needed to make protect guests from unscrupulous hosts, and hosts from larcenous or destructive guests.

Things began well, with Airbnb extending a million-dollar insurance policy to its hosts.

And then they focused on building trust by linking Airbnb to social networks (Facebook, Linkedin) so that Airbnb accounts are linked to people’s real identities:

“Trust is the key to our community.  There is no place for anonymity in a trusted community. That’s why we’re dedicated to providing our users with the best decision-making tools possible…

We believe that the right technology can help lay the foundation for trust in other people.   Today, we are proud to introduce Airbnb Verified ID—the next step for trust at Airbnb.  Verified ID provides a connection between the online and offline spaces.”

Sounds good, right?

Except when “building trust” means asking for unnecessary assurance.

Doc Searls quotes an Airbnb member for whom the “next step for trust” meant feeling deeply distrusted:

“The new verification process is insane and insulting. I have used your service for two years. My “reality” has been verified by my hosts and my guests: people in four countries have left feedback about their experiences with me. We have talked on the phone. You have my social security number from when you sent me tax documents. You have my credit card on file. I’m happy to send you my drivers license, but don’t see why you would need it, when you already have the rest. There is just no way I’m linking up my facebook account so you can datamine my friends, keep an eye on my day to day activity, or examine my relationships. There are enough safety checks on me through the relationship we’ve already developed. Please reconsider this stupidity.”

This for me captures a main problem with so many of the approaches to online trust:   Trust is not assurance.  Trust is the expectation that you won’t have to use the million-dollar insurance policy, not the assurance that you’ll be protected if the guest is a thief.  When you ask for layers of assurance on a relationship that was already trusting, you risk backlash:  We’ve done business together!  Why do you suddenly need more ID from me?

If you don’t buy that assurance crowds out trust, try this experiment at home:  Approach your spouse and ask them to sign a post-nuptial agreement.  See how well the argument that you’re just “trying to build trust” goes for you.

One of the keys to maintaining trust is to rely on that trust.  When you replace trust with assurance (asking your long-trusted spouse for a contract you shouldn’t need; asking a long-trusted customer for identification that you shouldn’t need), you crowd out trust.  Airbnb seems to be learning this basic lesson the hard way.