Preview sessions exist to reward members and to raise extra money. Entry is typically granted by showing a membership card or paying $5 to $20 at the door, and many groups let you join on the spot and walk straight in.
This is where the highest-value inventory moves: collectible hardcovers, complete series, clean textbooks, art and photography books, and anything a scanner flags quickly. Prices are the same as public days at most sales, so the fee buys access, not a discount.
Preview nights are also crowded and fast. Expect line queues before doors, table-by-table sweeps, and strict rules about staging piles or blocking aisles. Some sales ban scanning devices during preview specifically to keep the pace civil.