The 1913-S had 12 bids and was sold to a buyer with a 535 feedback score. One of the bidders for this coin had a feedback score over 10,000.
The ridiculous 1920-S had 11 bids and was sold to a bidder with a feedback score of 226. Other bidders for this coin had feedback scores over 4,000 and over 12,000.
The 1926-S had 44 bids and was sold to a bidder with a 5,080 feedback score. Other bidders for this coin had feedback scores over 12,000, and two over 1,000 each.
These counterfeits fooled experienced bidders. I suspect that the bidders for the 1913-S and 1926-S didn't look at the seller's other listings. By looking in isolation at the coins they wanted, they saw what they wanted to see and didn't see the red flags that were plain to see.
Here are some of the red flags:

The seller only has a feedback score of 31 (at the moment).

The seller had a bunch of non-numismatic items (purported Native American jewelry) and hadn't sold rare coins before. (The seller had sold some junk Morgan and
Peace dollars, and at least one of those lots
also contained fakes.)

The seller's listing admitted the 1913-S and 1926-S were polished. That admission deflected further inquiry, when it should have raised suspicion. Two similar scarce date but purportedly high grade polished coins should suggest polishing to remove evidence of counterfeit surfaces.

At least one listing (the 1920-S) was an obvious counterfeit. Never
never never buy from any seller who has counterfeits listed. Period.

The selling prices were far too low for genuine coins. The 1913-S Type 1 sold for $34, and a genuine coin in that grade range should have sold for $125-$175. The 1920-S sold for $78, and a genuine coin in that grade range should have sold for $1,100 to $1,700. The 1926-S sold for $315, and a genuine coin in that grade range should have sold for $6,600 to $8,000. If it looks too good to be true . . .
Chinese counterfeiters have centuries of experience. Remember, these are the same counterfeiters who have been making and selling counterfeit common date Buffs* in average mid-grades in counterfeit Whitman albums for decades.
*My file of descriptions and photos of counterfeit Buffs in mid-grades includes 1914, 1916-S, 1917, 1918, 1919, 1920-PS, 1921, 1924-PD, 1925-PDS, 1928-S, 1929-S, 1935-PD, 1936-PD, 1937-D, and 1938-D. Nothing, and I mean NOTHING is too small for them to fake. Ask our Canadian friends how many low priced, high mintage, common date 20th Century Canadian and Newfoundland coins they have faked.