An open bid system invites appraisers to bid on things they know nothing about. And I see it certainly in the RIMS customers I fired who were sending me offers to bid that were 50 miles away and might be from a strip mall to an undeveloped lakeside subdivision - two properties that I explicitly said I did not do in my RIMS profile. Further, I was limited to a single county apparently and RIMS offers and "upgrade" so you can buy into multiple counties.
The inverse could and should be equally true. If I am training someone to be a mineral appraiser, I should concentrate upon teaching them about minerals. We need more specialists. That C Store appraiser may need a trainee too. But the trainee needs to understand that they are working directly for a CG license and that they are going to be a niche player. If they want to expand into residential work, then they need to mentor those experiences under someone else.
All 4 of the mentors that I had were CG. My first inspection was a chicken farm, and I tagged along on 3 of them in the first six weeks, I also did 4 plexes, SFR, and executive homes under the direction of those mentors. I had an excellent relationship with 3 of those mentors and I survived the other. I would think the well rounded trainee would not want all their eggs in one basket. They should train under multiple experts and get different perspectives about the way appraisers work.