How does appraiser decide on NOI and CAP rate when it comes to valuing apartments?

[Nick Wu]

I am currently planning to do BRRRR on multifamily by improving ROI. I want to understand how calculation will look like when appraiser go for appraisal? This will help submit more meaningful offers.

PM, Maintenance & repair, vacancy: does appraiser use projected number (what % would they use?) or historical (how many month trailing)? 

Rent: how many month of rent roll does appraiser look back? Will late payment affect the income level?

Other costs: tax, insurance, utilities, lawn&snow, are these all historical 12M trailing?

CAP rate: what’s the best way to estimate what appraiser might be using? (1% +/- could make a huge difference in return). Any trustworthy data sources where I can use to estimate?