If something's wrong with a customer's program or something you sold them, then it's better to come clean and tell them if you can't get it fixed quickly than for them to find out on their own. They may say they are having trust issues with you initially, but by coming clean first the real issue will be with the program or whatever it is you sold them. Work to resolve their issue quickly and regain their trust in what you sold them and that will rebuild their trust in you. Trust, it's the foundation of any relationship. Model the way for others on how to rebuild, maintain and grow trust. It's the right thing to do.