If you have offered EMD and seller accepted the offer contract, depends on the terms and local law you need a rectified contract seeking for refund. 

I am not a lawyer, but I believe you are in the clear to send him a new check, non certified, as long as you keep the original, unopened and returned check that shows it was sent back as undeliverable. if he ever makes waves surrounding the sec deposit, you can then show the judge that you sent the original by certified mail within the legal timeframe. in addition, save the written correspondence showing he refused to accept a certified letter.

What margin should I accept?

Its the company you decide to hang your license with after you pass the test where you will really get the training on how to be a professional agent. 

and both offers have been accepted (motivated seller- Husband doing rental property and he has passed away - while working on a rental)  So both properties listed for 49,000 each...then $39,000.  

They want to move to another part of town but despite having applied at many places, they haven't been accepted, apparently due to low credit scores. 

@Jan Ferry-AxmanSelf-management of IRA owned properties (LLC or otherwise) is generally viewed to be acceptable in a limited fashion. 

In June of 2018 I passed my Maryland RE Test and now am a licensed realtor.

My question for "cash-only" sales are there any instances where a cash-only property would decide to accept bank financing? 

I'm really just looking to grow my investment capital and pick up some knowledge on the way to bigger more complex deals.So let's say hypothetically I find a piece of land that the owner will accept 20k for, but I believe the market value to be around 100k, giving me a rough margin of 80k to work with, before closing costs, marketing, etc.