Answer
Where can I get a diamond appraised in Johannesburg?
Pick the right tool for the right purpose.
GIA grading report. The international standard. The GIA does not have a SA laboratory, but several Bedfordview and Sandton dealers offer GIA submission as a service. The dealer takes the stone, ships it to GIA via insured courier, and returns it with the report 4 to 8 weeks later. The fee covers the GIA grading cost (USD-denominated), the courier insurance, and the dealer's handling. Use this if the stone has no current GIA report and you intend to sell or insure it as a long-term asset.
Independent gemmologist appraisal. Done locally, same-day or within a week. The gemmologist confirms the four Cs against current market value (using Rapaport benchmark or international auction data), photographs the stone, weighs it, plots inclusions, and issues a signed appraisal certificate. This is what your insurance broker actually wants. Names with reputations in Johannesburg include the appraisers attached to the Diamond Dealers Club of South Africa and members of the Federation of South African Gemstone Dealers (FOSGD).
Dealer trade-in valuation. Free, fast, and conflicted. The dealer is telling you what they would pay you, which is the wholesale price minus their margin. Useful for negotiating a sale to that dealer; useless as a "what is my stone worth" reference.
Independent gemmologist appraisal is the right choice for the typical buyer. The full grading-report context is in A reader's guide to SA diamond certificates. The Bedfordview corridor where most appraisal services cluster is in Where Johannesburg's diamond money actually goes.