How do most appraisers deal with half duplex

[Allen L.]

I am under contract on a half duplex in a really nice part of town. However, there are no comps in that subdivision for any half duplex going back 1 year, and there was one that was sold 17 months ago for a ridiculously low price, and 2 others sold within 24 months but I can't see the prices. Obviously they don't even factor in the 20%+ appreciation that we've seen in the past year, or close to 30% in the past 24 months. I love the house and sees potential and I want to keep it as a rental, but I don't know how it will appraise. How do appraisers deal with this situation? Do they go back more years (2 years in this case), broaden the radius, or use SFH as proxies?