Let your customers do the selling

This reminds me of the tips and tricks I've read about when you have customer complaints.

Especially in the early stages, really engage the customer. Get the customer involved in solving their own problem by telling them what the situation looks like from your perspective and if they have other ideas. Then over-deliver. Zappo's once delivered a pizza to a customer that misdialed them.

Those experiences are what convert detractors to promoter-evangelists.