Regardless of how you find them, try to interview at least three managers.1.

Through online research and word of mouth I originally contacted 12 PMs to interview and select the best for our first rental in Baltimore City, Maryland.

Have them do all the heavy lifting of going through leads, obtaining credit and background checks and then present you with the best of the bunch where you can then decide who to hold an interview with.

Definitely interview several of them and look for someone with Real Estate knowledge. https://www.napfa.org/find-an-advisor You might want to go to a local REI meeting and ask around.

Interview several banks with the same questions, put their answers on a spreadsheet to compare which has the best terms for your business.

As you continue to interview PMs, you'll add/remove questions and you'll begin to understand the flow of asking questions to highlight your main priorities.

Finally I interview them to make sure they see their job as a combination of looking after my financial investments, and keeping the renters (aka customers) happy. 

See who you like and remember you are interviewing your potential teamMember for a long term relationship.

Rob- why not interview a few builders?

MadFi interviews a variety of people at different points of their journey.