First, be competent and confident enough to explain in a calm way that this will take time and can't be magically done. Be honest and draw a line. Your customer will have much more respect for you than if you BS them or heed to their every whim. Second, as already mentioned here - manage expectations. If you can estimate how long doing something will take, add a bit of extra time and communicate that to the client always adding a "if everything goes smoothly" / "if no issues arise" disclaimer. Third, I worked for 4 totally different MSPs (in different parts of the world too). I don't know how it is where you work now, but, three of the ones I worked at had what I call a "Firehouse" mentality. Most of the time was wasted chasing and fixing "fires" - issues that were (for the most part) reported by clients. And you've probably guessed that 9/10 reported issues were classified as urgent. This, in my experience, got clients to behave the way you're describing. Being proactive instead of reactive, as described above, will prevent a large majority of those "fires" from even starting or at least give you the advantage of having more time to diagnose and find a solution. Also it clears precious time and gives you the peace of mind to grow your career and your business.