You're not simply choosing an MC number. You're attaching your customers, commissions, and reputation to another company.
Look at how long the brokerage has been operating, its authority history, insurance, carrier payment reputation, leadership, and any signs of financial trouble or instability.
A brokerage can offer a great split and impressive technology, but none of that matters if carriers aren't getting paid, credit is tightening, or cash flow problems start affecting your customers.
Ask questions about ownership changes, authority lapses, payment issues, lawsuits, or anything else that deserves a closer look. Talk with current agents when possible and pay attention to patterns—not just the recruiting pitch.
Your book may be your biggest business asset. Don't park it under an authority you haven't investigated.