Unanimous? Not as far as I'm concerned.
I'll authenticate for newbies, oldies, current listings, completed listings, private sales, non-linked sales/purchases, yard sales, buyers and/or sellers as long as the rules are followed, requests are polite and without a sense of entitlement or expectation and I don't believe someone is promoting their own items.
While some brand authenticators feel differently, I've seen several posts from various authenticators who seem to feel as I do.
I want to protect buyers from getting a fake and I commend those who want to make sure that any items they might consider listing are authentic. I don't necessarily believe that sellers should get professional authentications for those items they want to verify.
JMHO. Your mileage may vary.