BGS has no grade guarantee, so their buyers are just out of luck. Until they file lawsuits if they choose to. Class action that they are being duped by the appearance of having a fair grading company that is taking payola to give grades to the largest submitters would be one. They are getting skewered on Blowout.
https://www.blowoutforums.com/showthread.php?t=1297069
SGC is a small fry (submission numbers wise), but I believe they refunded the first few (unless the auctionhouse did instead) and then stopped refunding and closed their auto auth shop. They did recommend one scammed individual try to get restitution from the fraudster who submitted the card. Then they deleted the "Grade Guarantee" they used to have from their website.
But I'm guessing they're still liable for the guarantee on the cards that were graded while it still existed.
PSA was warned 15+ years ago that they were letting scammers submit cards, and stuck their heads in the sand and let the fraud continue. To me, that is complicit.