How do you know you have mercer?

Mercer is a well-known consulting firm, so if you're referring to having "Mercer" as a client or partnership, you would typically know through formal agreements, contracts, or communication from the firm. If you mean Mercer as a condition (like Mercer syndrome), symptoms would include specific health issues that would require a medical evaluation for a definitive diagnosis. In either case, clear documentation and communication are key indicators.