The mini-storage I've invested in has been a terrible investment.

The truth is that most agents are terrible, but you are likely not finding the good ones because you have a preconceived notion that they all suck.Some questions for you:If you are a cash buyer, did you show proof of funds to any of the agents? 

Absolutely I agree with you, Thats why the example is used was in terms of listing amount were the same while on Zillow said sold it said pending on Batchleads, Terrible latencies with both. 

He did a terrible job of fixing/renovating.

That is TERRIBLE advise!

So, why are there so many posts here on BP from owners complaining about their terrible service?

We've had terrible, terrible luck with new fridges.

While the system is great, my response rate is terrible.

Completely vacant homes show terribly.   

As I have been reading a lot of terrible experiences and stories about landlords getting burned due to tenants simply taking their softness for granted and especially taking advantage of a lot of elderly homeowners to live in the places for free and in some cases even filing lawsuits against landlords to simply make money out of them.