2014-09-28 UTC
# 
tantek in which case, as a user, after commenting (and presumably having their "normal" webmention rejected), they could check a hypothetical service like socialsearchme.com for themselves, see that they'd linked to B, and then see how many (if any) people they have in common, especially, if there are any people that B has linked to that link to A, and if so, presto, that's a "vouch" URL.