Being friends with clients is a bad idea?
In most cases - yes. Because soon you will either stop being friends with them or end wasting too much time for free.
I have a few exceptions in the past 20+ years, but in general - avoid making business with friends, at least without setting very detailed constraints where friendship ends and where business starts.
You can certainly have clients as friends and friends as clients as long as there's a clear understanding of the line between business and friendship. I've worked with some friends without issue and I've also lost friends over bad business arrangements.
I'm at a point in my career now where I would rather refer a friend to a colleague instead of work with them directly, but I know other freelancers who have no problem at all working with friends as clients (or clients as friends).
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