How do you handle difficult clients and scope creep?

Most freelancers eventually meet a tricky client. Handling it well protects your time and sanity.

Practical defences:

• A clear written scope up front: what's included, what's not.
• Politely flag when a request is out of scope and quote for it — don't just absorb it.
• Stay professional and calm, even when frustrated; your reputation follows you.
• Know when to walk away from a relationship that costs more than it's worth.

What's your approach to scope creep and difficult clients? War stories and wisdom both welcome.