OK. Buyer's premiums are premiums that are charged to buyers in addition to the hammer price. On top of the final price when the hammer falls. We're talking major auction houses here, but even many smaller auction places charge buyer's premiums.
Small, local auctions? Probably not.

FWIW: even the small, local auction house down the road from me, Eldred's, charges a buyer's premium. From their web site.
"A buyer's premium of 18% will be added to the hammer price to be paid by the buyer as part of the purchase price."

OK. That's enough off topic nonsense from me.