One thing I might suggest here is to target properties with small amounts of rehab first. 

If seller financing is your only finance option, I recommend targeting owners who are open to it rather than targeting conventional sellers and trying to convince them.

I'm targeting between 12-20% ROI.  

I always target an all-in cost of 70% of your ARV.  

I targeted a lower value home because I thought that if I made a mistake at least it would be a small mistake. 

Effectively, you discuss with your outside partner what their target return is and ensure that they get paid out their portion + target return at the refinance/sale/close/etc.

But if you focus on getting the systems and processes down and building them around your target market things should work out.

They can also target zip codes for hot areas, not just blanketing a zip code and sending to the first 1000 addresses on the list.DON'T expect return on your mailings the first, second, or third time around. 

Not ideal, our targets are 11-14% returns. 

So we usually target 3BR 2BA homes...LESS than $300k.