As the seller of these coins I am happy to respond.
The coins were sold to me by a fairly big and very experienced gold dealer where they would have been XRF tested prior to my purchase. I am not willing to name the dealer until I have carried out further tests and spoken to them directly as I don't think that would be fair. That said I think many people on this forum would know the name.
Two of the coins came with certificates and while these don't really prove anything it does at least state what the coins are supposed to be and everything else matches up as expected. The buyer was not happy with the coins he received and asked to return them, as a gesture of goodwill I accepted the return but until I receive them back and can get them tested more thoroughly I am still of the opinion that they are 22ct. Whilst I understand the Sigma isn't completely fool proof, as stated earlier in the thread specific gravity tests can also be misread and that appears to be the only test that has been done on these coins. There is also mention of a pawnbroker looking at the coins but no testing procedures were carried out at all beyond looking at the coins with a magnifying glass.
So far we have three coins as follows:
Five Laurels (40g) - Passed both the Sigma and specific gravity tests, not sure what the pawnbroker made of it but assume all is well as nothing mentioned
Platinum Jubilee (16g) - Passed Sigma test, had COA stating details of the coin and came from the same lot as the Five Laurels so I have no reason to doubt it other than the buyer's own failed SG test. Also no comment from the pawnbroker
Brexit Coin (8g) - Passed Sigma test, buyer/pawnbroker claims 9ct inscription on the coin which if true both I and the very experienced dealer I bought from have missed. If that is the case then of course I apologise but I would like to see this for myself.
As I understood the workings of the Sigma machine there are different 22ct settings that will apply to the different alloys that may be used which is why they have different settings for Krugerrands, Britannias etc. Happy to be educated on this if I am wrong of course, I am quite new to the Sigma.
Regarding the postage costs, the buyer agreed that he would cover the return postage. I wasn't aware that he was unhappy with this arrangement but as he has now asked me to cover it I will do so. I had planned to refund postage anyway should any of the coins prove to be anything less that what I sold them as. My personal opinion is still that they are 22ct gold and I wouldn't sell any coin if I wasn't confident of the purity. I am of course willing to be proved wrong though and will update the thread if that proves to be the case.
Without meaning any offence at all, I don't think the buyer was ever 100% happy with the purchase even prior to receiving the coins and I thought I was being quite generous in accepting a return which many sellers/dealers wouldn't do.