I would rather guess that it is the seller's pricing scales rather then anything about the pearls that makes the most of the price difference.
With neither grading or pictures precisely comparable between sellers, it's a dib in the dark...
It looks like the first strand may have somewhat higher lustre and a few more blemishes then the other. Circlee black pearls tend to have the brightest lustre and most impressive, other-worldly colors at their best
. And both strands seem to be of high quality.
I'd expect either to glow in the dark, frankly, with slight matter-of-taste differences in any aspect except... the quantity of blemishes. Clearly, even that is a matter of personal choice after all: I could imagine how someone else could make a more extreme trade-off between the two then I am inclined to.
Any chance you could order both and ... return? I am not sure how tasteful this sort of shopping is
but... so is the lack of standard grading for pearls in this blind online setting!
Frankly, I cannot make up my mind between the two either. The second strand seems to have well fewer blemishes (which would tip the balance, price and all) but then, the image doesn't show as much detail, so.. what could I possibly say for sure?!
My 2c...