It's a question for the folks you interviewed! They should be able to stand behind their conclusions. You say Agent(s), but is that two or three? I'm already skeptical of the agents you had, because if you were reviewing the units FOR SALE, as opposed to HAVE SOLD, I'd suggest you're looking at the wrong data. (For the record, listed property is not a comparable. Only sales are. Listed Property is good data, but much less so.).
Regardless of their methodology, they should be able to make you understand it. If you can't, find someone who does a better job of communicating with you.