just adding to posts.
i am a gia gg student( gemologist through gia) i used to have a local jeweler grade my diamonds and such, but then i found through my school that "any1 can grade or appraise, there is no law saying u have to have a cert." this is true but there are people out there that have taken courses and many grading practices b4 being cert. appr.
i joined ngcs collectors corner due to there grading ability.ngc and pcgs are the top known grading services.meaning (i hope)that they know what they are doing in the feild of coins.
in one instance my gia diamond appraiser appraised a cert. flawless diamond(that came with a cert. that i didnt give him just to see what he would grade it as)it came back as a si wich is 2 steps below flawless. so even those who know what they are doing have different grading ability. grading wich is an appraisal is subject to the grader.
gia grading is done with 3 people 1 looks then the other then the other, so that the best ideal grade can be found for said stone. maybe if ngc would do it that way it would even things out.(maybe they already do i dont know). just stating what the gemologist do:)