The person who originated the program promised too much and got behind on filling his orders. Or, some people became too impatient or anxious waiting to receive their order and turned in a complaint. The complaint is sent to a Postal Inspector who, in turn, sends a form letter to the person conducting the sale of the program, asking it be stopped. I've seen a lot of GOOD mail order programs stopped because of one person who complained to a postal inspector. Just one dissatisfied customer can ruin your mail order program, so keep everyone happy.
Honest mistakes can happen, but remember the customer is always right.
Work to fix any mistakes immediately and keep the customer informed of all progress. This, combined with honest mail order programs, will prevent those Postal Inspector letters.