Tell him to hire his own mold person for testing and advice. You did not perform the test and have no first hand knowledge, nor are you the seller’s consultant. I certainly wouldn’t offer my services to the seller as I will only ever represent one party in the transaction.
“I’m sorry, I can’t help you with your mold questions. I did not perform the mold testing on your home and I’m not in position to offer you advice on the matter. I would advise you to engage a qualified mold consultant of your choice to advise you regarding any questions you may have regarding mold.”
I wouldn’t worry about the SOP, I’d worry about shooting myself in the foot! If you make representations about a mold test you didn’t do it could come back to haunt you, and the buyer may have a legal case against you.
There is plenty of mold misinformation on the internet. Don’t get involved.
I agree with everything above, for both ethics and liability reasons, plus, the protocols followed during sampling are important and you have no control over what the client did.
If I were a seller I wouldn’t be too open to negotiating points related to sampling done by the buyer. I’d need to see the results of professional (neutral third party) sampling before I considered making allowances for the results.