Many things are lawful; but not beneficial. Many things are lawful; but not trustworthy. It is why USPAP has the ethics rule: The ETHICS RULE sets forth the requirements for integrity, impartiality, objectivity, independent judgment, and ethical conduct.
An individual appraiser employed by a group or organization that conducts itself in a manner that does not conform to USPAP should take steps that are appropriate under the circumstances to ensure compliance with USPAP.
Disclosure is the way to handle the inherent conflict of being a Realtor and an appraiser, not only to the client at the time before accepting the assignment, but in the body of the appraisal report. In addition, if you know the Realtor handling the sale and have or had a past business relationship with that person, it needs to be disclosed.
Personally, if I were a buyer, I would not trust the appraisal report by an appraiser who also is a Realtor to perform ethically.
As a buyer, I might feel the same. However, some appraisers can perform ethically with a dual license, some unethically without the conflict. I personally would have an issue with appraisers trying to solicit referrels from realtors whose property they are doing a purchase appraisal on.
However, this is not a complaint stemming from a borrower. If the property were overpriced in contract, the borrower was not put in any conflict by the appraisal ( I wonder what the outcome was, did the price get negotiated to MVO and did the deal close?)
If a borrower had a complaint regarding a possible conflict of interest, that would be different, whether warranted or not. But this complaint is coming from a realtor, perhaps to retaliate for a MVO coming in "low." Since hey are buddies, the realtor must have known for months or years about the OP dual license...why was it not a cause for concern until a SC price did not come in?
I bet if the SC price was met or exceeded, this realtor would never have complained about a conflict of interest. That is something the OP might be able to clarify more.
The OP is bringing out the consequences of what can happen and it is making a difference in trust.