There's no better way to earn trust than to show someone you care...with no strings attached. As Seth points out, following-up with your customer is hard, especially when there's no agenda like selling some more, or asking for a referral. Calling someone just to see if everything is okay seems awkward, unless, of course, it's a friend. Then it's almost natural.
And, isn't that what our business of hospitality is about? Trust and friendship?
So, do something hard...talk to and do some things for your customers with no strings attached. Incidentally, this approach works extremely well with your employees too.