She will receive the initial "buy" amount that we agreed on, a portion of which is going to be paid up-front in order to bring her mortgage current and give her enough to move out to Ohio, and then a percentage of the final sale amount.The reason this flip works is because we are avoiding going through two purchases and also avoiding financing fees from a HML on the purchase of the house, since the owner will still own the house during renovations.Since she doesn't own the house outright, this isn't really "seller financing," but maybe more like a joint venture?

In this instance, the IRA is subject to a small amount of taxation on the percentage of income derived from the non-IRA (borrowed) money. 

All of your reserve percentages are too low.

The properties I have been analyzing seem to have a low percentage based on the asking price.

The interest rates are higher than conventional loans and a small percentage of the loan called "points" is paid on closing.

Is there a rule of thumb as far as percentages?

I am interested to hear what percentage of deal you typically like to buy as an investor for a flip property.

I was thinking 12% interest, and a percentage in the ownership of the deal? 

You can interview other agents.However, in reality, there are a good percentage of agents that either 1) Will not know how to analyze investment 2) As you said, are not savy with off market 3) Are not familiar with real estate investing in general.Not to say they are not great agents in finding a home for the general population.

How many units is this property, and what was your down payment percentage....there is a lot here not adding up. 1 unit FHA loan limit in DC is is lik $725k, so even at 10% down, we are talking about $800k property max on FHA.If its 3/4 units, these properties are not going to meet the FHA self sufficiency test.