Appraising is a very challenging profession, especially in declining markets, and in most states there is stringent licensing and education requirements. You can certainly call the appraiser to discuss the final report, but the truth is you don't have any control over market -- you have control over how you price your home and its condition (I do tell sellers to treat an appraisers visit as if it were a buyer tour -- sparkling clean and a cookie scented candle!). The report will adjust each comparable as to size, number of baths, views, etc. Appraising when there are not many comps requires different appraisal approaches that a professional will use, not just comps are reflected in the report is my guess. Have the appraiser walk you through the questions you have, but be diplomatic and view it as a learning session, appraisers don't usually change their opinion. You could also have another appraiser conduct an appraisal and produce a report, they may have differing opinions.
The "ethics" part of your question is that the loan originator cannot appear to be biasing the appraiser -- we all have our separate jobs to do in the transaction; the appraiser does appraisals, the mortgage broker provides lending, agents do the communicating -- and if we all do our jobs right, with ethics as the rules, we won't need to bring in the lawyers.