There are a lot of variables here.

There're many variables involved, but it mostly comes down to what are your goals for the investment and what level of risk are you willing to endure. 

Cash Flow = income - expenses Income is rental income, calculated net of vacancy.Expenses include: Fixed Expenses + Variable expensesFixed expenses: PITI (Principle, interest, taxes, insurance) + Utilities + other (HOA)Variable expenses: Maintenance, Capx, Property ManagementARV and Refi % are factors used in determining how much cash out of pocket you need for the deal, which will help you determine your cash-on-cash return.

When that doesnt happen, the listing brokerage keeps their entire commission.Sometimes a listing agent and seller may enter into a variable rate commission in which they lower their commission if there is no other agent involved.

Additionally there credit score is low due to previous mortgage history amongst other variables.

I have seen banks be really variable on other lending products though and the relationship matters a lot too, so it's probably worth talking to a few if you get the point where you need hard data. 

And pricing is almost exactly the same, because they get the variable rate vs 10-yr fixed.Separately, one thing some CRE investors forget to check is what their index is - prime or LIBOR.

In the end, there's a lot that's out of your control, so best to add a large layer of variability to any subjective number, such as ARV, rent, and repairs. 

The bank has approved me for a HELOC of $100k with 4.5% variable interest and the origInal plan was to use the heloc to put the 20% down on the new house.

I'm wrong dozens of times every day but it seems like this situation has too many variables.