Appraiser

An appraiser is a licensed or certified professional who develops an opinion of a property's value, usually for a lender. For one to four unit rentals, the appraiser can extract gross rent multipliers from comparable rental sales and apply them to the subject's market rent as a supporting check on value.

Lender appraisals of small rental properties typically include a rent schedule built from comparable rentals, and that market rent is the figure the lender relies on. If you screened a property at a GRM of 10.4 using the seller's rent and the appraiser finds lower market rent, the appraiser's GRM on the same price will come out higher.

The appraiser's value, not the contract price, sets the loan amount. When the appraisal comes in low, the gap is often visible in the GRM comparison: the subject was priced at a multiplier above the comps. Reading the comparable rent and sale grids in the report shows exactly where the difference came from.

Further reading: Appraiser on Wikipedia.