And also: Let your Lawyer handle your legal business.
Yes, anything involving threats or warning should be handled through a lawyer. Obviously normally commercial activity involves eg contracting and you don't normally need a lawyer for buying and selling. Anything adversarial though, you need a lawyer. Absolutely, anything involving claims of intellectual property infringement (in the UK you can bring a claim for debt recovery up to £5,000 in small claims court without needing a lawyer). You don't see WotC games developers sending out C&D letters, do you? They refer to their lawyers. Their lawyers often tell them "don't do anything" - unlike TSR, WoTC/Hasbro have real lawyers who seem to know their stuff very well.