Was thinking of the things that are absolutely essential for my line of work, at least for my own operation working with WordPress and web development. Some are specific to working on the Web, and some probably would apply to any line of work. If it is absolutely necessary to test something on a user site, it must be a private/development site, and the user (site owner) must agree to a no-liability disclaimer. User feedbackAlways listen to user feedback, even when negative or harsh. And then I make sure to keep good working backups of everything just in case.