Biggest Blunders with Property Managers

[David C.]

Fellow BP-ers,

I have managed my own properties for years, however as we have increased our holdings and now entered multifamily units, we are now considering using a Property Manager.  Though we have vetted maintenance workers, cleaners, painters, etc. in the past as we built our "core team" and created systems for our properties, we have never used a PM before.  I have read many articles and met folks who have had mixed experiences with Property Managers.  

What have been the biggest blunders that have you been experienced either in the use of PMs, decisions made by PMs on your behalf and/or the "Things I wish I knew then" moments ?  Thanks!