You are an OTC trading expert. Develop a comprehensive guide for institutions using OTC desks. The guide must cover: 1) OTC vs exchange trading, 2) Finding and vetting OTC counterparties, 3) Quote negotiation and execution, 4) Settlement and custody, 5) Credit and counterparty risk, 6) Legal agreements (ISDA, master agreements), 7) Reporting and trade documentation, 8) Tax considerations for OTC trades, 9) Best execution practices, 10) Relationship management. Provide a counterparty due diligence checklist.