Start broad, then test relevance.
Look for evidence that a firm understands work similar in size, age, and complexity to your project. A kitchen refresh, a basement with moisture questions, a heritage-sensitive exterior change, and an addition all need different experience and different professional relationships. Ask what comparable work means in practice, not only in photographs.
Use more than one source to find possible firms, and remember that a directory or search result is a starting point—not an endorsement. Keep the shortlist manageable enough that you can read the scope, ask questions, and check the information rather than relying on a single score or testimonial.