Ask HN: How to do freelance work that is reclaimable?

Most of the projects I see, their coding depends on the outsourced company it started. I would like go into consultancy business but when things go side ways and it comes time to leave my customer, I would want them to remain happy.

Here, I wonder if how other companies are willing to take over the existing code? What should I do best to make transition easier for the project itself for encouragement of new team taking over?

Thank you for thoughts.