authenticity of pearls

Hi,

I am looking at bidding on 3 different pieces on ebay all from the same person, voctoriaowens. She claims all 3 pieces are from an estate sale in Savannah, Georgia. 2 are supposed to be Mikimoto's and the other is not a Mikimoto, it has a different box from London and the pearls are not completely round when I look at them in an enlarged screen. It has a diamond and platinum clasp.

She states it is from the 1920's. If I won the bid I would send the "Mikimoto's" to Mikimoto for an appraisal and she said if they were found to be NOT real, she would take them back and give me a full refund. I know this is a lot.... but if you have time could you look on ebay at her 3 pearl strands and give me your opinion based on the pictures that you see?

Could the non-Mikimoto strand be natural pearls? Do you think the Mikimoto's are authentic? I can see that the clasp is real. I just don't want to get swindled but I would really love to own a vintage strand of pearls.
Thanks so much...