Help pricing grandmother's 3ct diamond ring?

[artdecolover71]

wow, stunning and classic! SO glad you sent it to GIA!

 

[kenny]

The most interesting part so far is that the first appraiser got the weight wrong—it’s actually 2.85 ct!

If the appraiser had the stone loose that's awful.
If, as I suspect, the diamond was set in the ring this carat weight difference does not reflect poorly on the appraiser.
If you read the appraisal carefully the specs being only estimates (since the diamond is not loose) is probably in there.

If you can't weigh the diamond alone you can only guess at the carat weight, so it's harsh to say 'the appraiser got the weight wrong".