Question about appraisal for multi fam

[Amber Stout]

Hey all! I want to start by thanking you all so so much as you've all provided me SO much value and I'm so grateful for this community. 

I have my first multi family property under contract right now for 231k. I just got the inspection/renovation estimate to be about 70k just to be "livable" which would include no upgrades. ALL multi family comps that I've pulled were under 300k and in MUCH better condition. That said, I have went back to seller to propose much lower sale price. He is claiming that the house is going to appraise for 400k+ after renovations and is backing that by using single family comps. Single family do comp higher than multi family in this area. 

Question is when an appraiser appraises this thing, are they going to use single family or multi family? If multi family, there's 0 data to support his claim so that makes no sense. 

Thanks so much all. I appreciate you.