That is frustrating but it is also an opportunity. 

It frustrates them.

I understand the frustration of fixing other people's messes.

After way too much frustration, I decided to switch property managers, but the process has been a nightmare.

This is an expense you want today, that will save you a ton of time, money, mistakes, frustrations later.

At first, it was frustrating.

It sounds like you're in a tough spot with this flip, and I can understand the frustration.

I have helped others with little benefit to myself and I know it can be frustrating when they don't follow through. 

Sad and frustrating trying to buy from them. 

You treated them as part of your personal finances when you wanted to lay your hands on some money BUT want to think of resulting debt as part of the business and are frustrated that the rents aren't covering that debt.