In an internet search I found that Miki currently sells "silver seal" quality pearls under the Sea Magic by Mikimoto brand at a chain jewelry store in the US. "Silver seal" refers to a lower quality than A grade pearls, as you can see by the photos of the nacre irregularities. These pearls probably were purchased before Miki started selling under different brand names, including Blue Lagoon.
These are certainly pretty pearls, as Caitlin said, excellent luster and meant to be worn and enjoyed!
However, without knowing the provenance, there is no way to to tell your customer FOR SURE that they are Mikis-------only that it seems likely------IMHO------