honestly what people assume to be bias really isnt. an appraisal is an opinion of value, so different appraiser will have different values. you cant choose your appraiser(before you could), they get assigned the job. they get paid a flat fee whether your value is high or low so they dont care what your appraised price comes out to as long as they can explain it. they usually dont over value it because that could lead to overinflated fraud(the reason you cant choose your appraiser anymore, banks went with their go to appraisers who appraised high so that they could get people to qualify for mortgages and sell the mortgages off) which they dont want to deal with.
so most of the time appraisals will come right at the asking price because they are lazy and just want to do a fast job to move onto the next one and can justify it with comps. other times they will actually run all the adjustments and do a good job and if its highly upgraded then it may come in a little higher or if its not in best presentable condition it could come in lower depending on what the appraiser thinks the property is compared to comps.
doing an appraisal is more complex than just running comps and comparing pirce/sqft like most investors and realtors do. you have sqft living, sqft land, easments, bed count, bath count, garage vs carport vs no onsite parking, condition of home, location, etc. again its just an opinion of value, so one appraiser might think there should be a 10000 adjustment to one line and another might think it just needs a 7000 adjustment. some might look at your messy property that just needs a new paint job and flooring and adjust the condition lower than someone who knows thats all it needs.
so to say an appraiser is bias doesnt make sense to me because they gain nothing by intentionally lowing your value because of skin color. they just want to get paid and move on the next one with the least amount of work. if you said some appraisers are incompetent, then yah i would have to agree but you cant choose which ones you get.