Larry garfinkle not sure if he's on BP but he is on Facebook.

Check reviews on BiggerPockets, get on Google and check for reviews, ask for referrals from current and past clients, have an inspection done on the property, check with other property management companies in the area to ask about the one that’s managing your property, ask them if they feel the rent amount is priced right or if it’s to high for the area, get in the the local real estate Facebook groups and ask members if they know of or have had any experience with the provider and even ask them to PM if they can share any insight about them.

They are your friends on facebook.

Since you are looking for buyers I suggest joining as many networking sites as possible, Facebook, Instagram, and an app called meetup and focus on any groups involved in real estate, especially in your areas of interest. 

They are posted on our facebook page and here on BP when the details for the event are available. 

Currently I'm posting my available units online through apps like Zillow and social media like Facebook.

@Sviatoslav Gulko if you're unsure about the concept of bird dogging, I have a group on Facebook called Bird Dog Real Estate and YouTube channel called RealTalkkWithEli where I explain the idea behind it

Craigslist; Facebook Market; bandit sign; real estate meet ups; auctions to name a few.  

I don’t have any experience / knowledge other than reading books, BiggerPockets, Facebook groups, and overall research.

They all have their pro/con...I personally just shop on sites that a typical tenant would shop on when looking for a unit...so that includes Zillow, Trulia, Craigslist, Facebook etc etc etc..... compare apples to apples etc and use the actual real competitors #'s...not some number Zillow says it should rent for etc