Martin, if this is about a sales cycle, just stay in touch with the customer. Over-promising/under delivering is one of the surest way to increase churn. Not only that, but I'd start digging into that competitors customer base. If they have lied to one customer, they have lied to others. Good way to pick up new customers.
Remember that this is a very small world. I remember which sales reps and vendors are good partners and which are not. I both buy and talk about the sales reps and vendors who are ethical. I avoid (and tell others to avoid) those who are not.
Keep it clean :)