John’s pics are obvious, yours seem border line to me. Border line means further e-val is needed you did the right thing IMHO. (especially with the back ground you stated)
If the panel is in the garage on the outside wall (block) instead of on one of the sheetrock interior walls, the discoloration probably would not be from Chinese drywall, but from another sulphur source. The evap. coil doesn’t look like anything I’ve seen in homes with Chinese Drywall.
You can tell them that there are indications that the home may contain some of the bad product, and refer them to a testing company that uses an XRF gun.
I just referred one like that last week where the symptoms were very borderline. The company that came in found that several of the rips in various areas, plus the two small bedrooms contained bad product. The majority of the 2100 sq. ft. home was fine.
Actually the small lines look completely black to the naked eye the photo was taken with a flash that resulted in the green color. This unit is four years old and I don’t have a way to determine if that is the original coil. I will now actually beg your forgiveness for falling silent on this post. I have concerns due to communications from parties involved in the transaction and do not wish to put any more information out in a public forum. The plot has thickened somewhat and while I will eventually post the result, for now this needs to rest.