Yes, AUCTION is a Scrabble word!

Letter values in Scrabble US: A 1, U 1, C 3, T 1, I 1, O 1, N 1.

Is it a valid word?

AUCTION is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a variety of bridge in which tricks made in excess of the contract are scored toward game; now generally superseded by contract bridge
the public sale of something to the highest bidder

Also: auction bridge, auction sale, auction off.