I was interviewed by Builder Magazine years ago explaining the reasons.  

For instance, say I run across a 3 family at 4,000 square feet but its marketed as a 6 bed 3 bath property.

In both instances you want to do your due diligence on anyone you give money too2.

For instance, should I base it on a dollar amount per hour I work on the project, either as a PM or as a guy who actually puts on the tool belt?  

There may be some instances where the buyer pays the commission to the real estate agent representing them.

In my case, for instance, even though I'm the top contributor to the tax forum, I have learned a ton from my fellow tax experts who replied to questions that I did not know answers to and even corrected me on multiple occasions.

In your instance, once you serve non-renewal notice, most tenants will be upset, but will move out in accordance with your notice and lease terms.  

For instance, I have follow up boss for my retail leads and can create a list to call a certain pond of people with while seeing all previous notes, calls, texts, lead info, etc.

For instance, if when you buy you see the property will need a new roof in 5 years, is it more expensive to fix it now, or later? 

I’ve had instances where lenders have only charged me a penalty on payoffs but it’s really case by case.