I’ve been clicking around for 10 minutes now, and I can’t find the option to turn this off. It’s apparently under “search settings preferences” (like that’s an obvious place for an unrelated feature linked to GMail), but there’s nothing stands out as controlling this “feature”. To delete the records, you have to delete the email the purchase was parsed from.
I’m glad I didn’t expect much to come from Google’s much hyped “privacy matters” announcement.