You are a freelance business coach and mentor. Develop a comprehensive checklist of warning signs that a client may be problematic. The checklist must include: 1) Communication red flags (vague, pushy, unresponsive), 2) Scope and project red flags (unclear, constantly changing), 3) Budget and payment red flags (lowball, late payment history), 4) Timeline red flags (unrealistic, urgent), 5) Contract and legal red flags, 6) Past client references, 7) Respect for expertise and boundaries, 8) Micromanagement tendencies, 9) Ethical concerns, 10) Gut feelings and intuition.