They want retail price for their houses and have a plan to sell  2-4 annually on the MLS.As they won't owner finance and I can't offer any more, do you know of any more advanced techniques that would allow me to pay a higher price for the properties but still have reasonable cashflow?

At that point, you could start using the BRRRR method until you reached your goal of properties.

There was another method you can use Being that you are dealing with criminals you may wanna see about your local police station serving the paperwork ( oddly enough many do this for a nominal fee) because this will really upset these guys if they see somebody that’s in law-enforcement coming out to the house and serving the papers. it will make them very nervous and they may want to leave altogether or comply

After I get my 10th and final loan, I will definitely use this method. 

Current Situation:My offer has been accepted and I have 9 days of due diligence remaining.My Ask:Without reading “The Book on Investing in Real Estate with No (or Low) Money Down” YET...What are some methods/strategies to lower my upfront costs for the down payment, while not getting beat up on interest rates?

Thank you in advance for all of your thoughts and advice.

I would like to use the 10 conventional loans myself but at that rate I could only do 2 deals a year when you take into account the seasoning period when using the brrr method.

. - a good zoning attorney will be much more helpful than a contractor's advice.I still recommend you to look for a contractor beforehand - good contractors are booked way in advance!

@Medi Sarwary I can share with you my experiance doing the BRRRR method (Actually I do a slight variation, the BARRRR method (A=Advertise, you do this for tax write of purposes if needed to write off more of the rehab cost right away.

Thanks in advance!!!