Promote your track record
While past performance is not a guarantee of future performance, it is the best predictor. Sell your track record to the customer.
Source: Sales trainer Dean Goettsch
Talk about your successess and the benefits your other customers experienced. But also talk about the problems you've encountered along the way and what you and your company did to overcome them.
Strictly talking about successes can create a rose-colored picture and might raise some doubt within prospects. A balanced discussion that examines your successes and how you quickly resolved problems will give the customer a good idea of what he/she can realistically expect and help raise his/her comfort level with you.
Your straightforward manner also increases the likelihood of getting the sale.