Peridot Ring ?

by heather
(cheshire)

I have sold a peridot ring on ebay. I took it to 2 jewellers who told me it was 9ct gold. the buyer is disputing this. he says that it's not hallmarked and has either 308 or 306 inside.

I didn't check if it was hallmarked because the jeweler had told me. Does 306 0r 308 stand for anything please?