I've asked Apartments.com about certain features, like having the apartment numbers actually listed in numerical order instead of randomly and being able to email/text tenants thru Apartments.com.

If they aren’t the same price to rent/buy then you have a pretty major error by a “real estate” company calling them “the same in all aspects”.

In order for need to find cash flow in a given property, I often have to bring the purchase price down several hundred thousand dollars lower than what it’s at (e.g. from $600k down to $100k).This is obviously unrealistic and therefore I feel like I must be drastically over-conservative on some of my calculations.I have compared my custom-designed calculator to the bigger pockets calculator and it calculates similar values, so I know it’s not a coding error.

Especially if there are numerous buyers are interested. 

I am not an agent but I was under the impression that you can't share commissions with others.You want to speak with an attorney but there is a good chance that if you are doing the actions on behalf of the LLC/S-Corp(as would be expected by an agent) that you would likely be sued personally as well.I would look to get proper Errors and Omissions(E&O) insurance.

That happens when no opponent reaches base — not by a hit, or a fielding error, or a walk.

Trial and Error my friend.

Check for errors -- they're not all that fancy!

Used the loan estimate while it was processing as my proof of funds for the new purchase.I used HELOC that was closed/paid off with this cash out as down payment for numerous investment properties over the years.

More likely, it never actually closed and it was marked as such either prematurely or in error.