Here are some of my thoughts on this auction:
The seller must be in the business to make money. A double natural strand for sale is a rare event. The top auction houses in the world would sell it at best prices. If it is as claimed, it is worth promoting. It is worth getting it into a catalog. Why wasn’t this done? That is where the big, legitimate money would be.
If this necklace is truly “natural” pearls, a sterling silver clasp devalues it. It should be gold or platinum and would certainly be worth the investment.
They do not look like freshwater pearls so what kind are they?
If these pearls are truly “natural”, then there should be some kind of story, history, or provenance. When and how did they appear to this seller and how does the seller know they are “natural”? Even if the story is that the seller found them in a second hand store in a faux pearl basket, as happened in the case of some quahog pearls a few years ago, there need to be a good story. If there were a good story, the seller would be using it to up the bids!
Even more important than a history, if they are natural they should have some kind of proof, like x-rays and an evaluation by a lab. The expense, like the expense of a good clasp, is worth it because the return will be huge.
The seller says they can “guarantee” that the pearls are natural. What does that mean? Why not present the proof in the auction? Any kind of proof would send the bids through the ceiling.