To make customer happy you don't have to build reliable software. Corporations are not machines, there's a lot of people with their own interests, who make important decisions. You have to make these people happy, first of all. They can be bribed, convinced or fooled to achieve the desired outcome for your business. And if something bad happens, you have to dodge the bullet together, because you are in the same boat. So you blame other contractors, hackers or the guy who left the customer company some time ago, and do a lot of other things to convince the customer management, that it's not your fault, you actually saved them from bigger losses somehow and you can help to build better software. And they won't be happier, but they will think that you are good guy trying to solve their problems. And that's the only thing you need to sell another contract.