Yes, you might discover that your average price is accurate, which is just fine for a reporting site. But beneath that there could be some structure, for instance there might be blobs of houses that your model makes too cheap vs reality, and blobs that are too expensive. If those are identifiable, eg via some sort of local knowledge, you might find that people will sell you houses that you've marked too high, but you can't buy the ones that you've marked too low.