It seems that there are GIA, EGL and AGS certifications for diamonds. Are they all equivalent? Can I confidently buy a diamond that has been certified by EGL as being of the same standard of evaluation as GIA. I was told that this may not be necessarily true. Understandably, I can have the gemstone independantly appraised. Why would a seller have diamonds certified principly by one laboratory? Do they get better costs per piece evaluation or does one lab bias ratings a little higher than another for a given quality of stone. Are these evaluations standardized in some way or is there a larger component of subjective evaluation - making all of this some what dubious?
My concern is I may be buying a diamond of lower quality but rated higher by the EGL certification.

My concern is I may be buying a diamond of lower quality but rated higher by the EGL certification.
