I have good credit 800 and a great w2 job with 2 other investment properties (in a different state).Should I just accept the 25% down, or will a conventional bank even offer a 15% down?

How much were you charged for replacing the tile?

Unless vets are considered to be so special that credit scores do not matter a 500 score will be no where good enough for any conventional bank loans.I would rent, with luck you may find a mom and pop landlord that does not care, then work to repair your score over the next couple of years.  

My credit card only charges my Netflix and is paid off in full to maintain 3 lines of credit.

I mean I used to work as a licensed contractor and for an estimate I would charge $47.00 per half hour of my time , still quite affordable if you ask me Plus that would put me first in line to contract with the cash buyer.

I charge the buyer let's say a 5k down payment to get in the house plus I profit off the difference in mortgage/rent rate right.

I've seen them charge anywhere from 1k-3k. 

Will she charge me or can I just cut her something out of the deal?

I found some cold callers in FB groups charging only $4-6/hr.

Not for free, I would always charge them.