@Mike Alber It is unusual when the seller has a contractual agreement with a broker; trying to sell for cheaper price outside the listing agreement. 

Also, consider that it is a highly unusual scenario to be able to get 100% funding.

Rents usually go up each year unless they're really maxed out, so it's not unusual to see increased rents each year when there is turnover each year. 500k for a property generating 4400 is pretty good (although I have no idea of the location or condition of yours), I am going to list a SFH soon in town that should rent for 4350 and it will list for about 520k (excellent shape) so you're not far off. 

An attorney will be able to answer with state specific information, but unless the property taxes are outrageously expensive it would be unusual for Lamar to allow it to get to a tax sale.

That’s very unusual as you can’t get one without a contract.

Hi @Anthony Wilson - In addition to paying off or making payments on time for the creditors on your credit report:There are services which log payments to your credit report for things that unusually don't show up, like rent payments.

Unless your Realtor had an unusual situation, it might be time to look for a more responsive Realtor.Also while on this subject, I can tell you from years of experience...Have your Realtor present your offer in person.  

I know this is an unusual situation and would appreciate any feedback...

She has an unusual property that includes about an acre of land behind her house. 

I don't think there's anything too unusual here.