The reasons for a bad AVM vs a bad appraisal imo would be different. The AVM and the appraiser both have access to the same data. The appraiser qualifies the data, the AVM can not do that on a personal each one analyzed basis, but by a rote programming basis. And the rote part is the flaw...maybe in future years AI will replicate human experience and judgement but we are not there yet .For example, the fannie CU comps satisfy their rote within a mile within X % sf, but can range from good to mediocre to terrible comps due to various reasons.
If an appraisal is bad, other than a one off event, it is either the appraiser was not competent for the assignment or the appraiser set out to mislead/ inflate value - either way especially the second the clients should not be using that appraiser -
The other flaw with an AVM is the AVM concludes X $ value, is that a range or a point value with a confidence score around it ? Either way, who on the client or user end gets to choose the value from that AVM or whether to rely on it, order another one? idk but seems a murky area..