Seller wants to get appraisal to determine selling price

[Matt Sauls]

I'm working an off-market deal on a 3 unit multi-family property directly with the seller.  We stumbled upon her in a discussion of her primary residence (which did not sell).  She said she had an appraisal done and that was her determination for selling price on her primary.  After 180 days on the market and some interest but no one getting over the finish line she did not sell because she wouldn't budge much on her price.

In the discussion we learned that she has a 3 unit multifamily property.  We stated our interest.  After a few days she responded she would be willing to split the cost of an appraisal to determine value.  She already stated a selling price which is in her mind.  At that price because of the income and expense ratios the deal does not work.  Her equity position is substantial so it's not driving a listing price decision.

I would have no issue splitting an appraisal if I had a good sense of how they determine value.  Here are my questions.

Is the appraiser's value going to be market based or income based?  Are the rents she is currently achieving going to drive the appraiser's number or is it simply the price the 3 unit property sold down the street as a closed comp regardless of income?  Thanks for your comments in advance.