Financing question on MF deal

[Dave Lawrence]

OK so here's my situation. I did a cash-out refi on a property 2 mos ago, took out $100K, then went house shopping in another state.

I found a 3-property deal down south in a growing market. List is $145K for two duplexes and a SFH, which lease for $2125/mo total. All utils are in tenants names, and rent rolls indicate they're decent, blue collar tenants.

I offered $120K cash. They came back with $145K. I offered $130K cash. They came back with $145K, though they'd be willing to carry the extra $15K at 5-6% themselves "for a few years until it's paid off or until I refi."

I'm no quant, but I can run basic numbers. My gut reaction is that doesn't make sense, that I'd rather just do conventional financing at that point. I'm not 100% convinced the properties would appraise at $145K, in which case I'd be under water from the jump. 

My thoughts, in no particular order: 1) walk away; 2) conventional financing at their asking price, understanding that if the properties appraise under their asking price I either bite the bullet, they come down, or I walk away (and am out the cost of three appraisals). 

The third option I'm considering: agree to their asking price, but they'd have to carry the extra $15K for 3 years at 0%. I feel that moves a bit of the risk off me. My intent all along was to refi these and pull cash back out and do it again, but...  

Thoughts from the pros?