How's my property manager doing?

[Jason E. Smith]

I own a handful of rental properties and I have two property management companies watching over them.  How do I know if my tenants love or hate my property managers?  I don't want to go knocking on every door, I don't want them to know who I am and I don't want them to have my home address.  Do I reward them for completing a survey?  Any sample surveys would be greatly appreciated.  Thank you and Happy Investing!