Agents usually search by price and work from the outside parameters (distance, date of sale, size) that they think appraisers are allowed to use. They are using the answer to the question (price) as the primary search parameter. They are approaching the question of value from the perspective of what the appraiser can nominally support.
Appraisers are supposed to work from the most similar parameters and only expand outward as necessary. The value is the answer to that question, not the primary search parameter.
These are two completely opposing approaches to picking comparables, each reflecting their different roles. The brokers look at MV in terms of 1 willing buyer + 1 willing seller because that's what it takes to make a sale; whereas the appraisers look at MV as the most probable via many buyers and sellers.