My answer would depend on the:
A Situation
B If a relationship exists
No shows are always bad news. Even if it’s a trusted client, it hurts to have a hole in the schedule. Likely most providers won’t tolerate a No Show from a new client. I’d say most will not let that person book again.
I can be lenient on cancellations. I know life happens so it isn’t too big of a deal. I have every text message in my phone, so if somebody cancels more than once, I know about it and act accordingly. My cancelation rate is very low, so this isn’t too much of a problem for me. I always ask that when a client knows they are canceling, to let me know ASAP.