What is the difference between an auction estimate and a price in a guide?

An auction estimate is the auction house's opinion of what a specific item in a specific sale is likely to bring, usually given as a range. It is based on the house's experience with similar pieces, the item's condition, and the expected audience. Some houses set estimates to attract bidding, so the actual price can land below, within, or above the range.

A price guide value is usually more general. It may be based on past auction results, dealer asking prices, or editors' judgment, collected over time and published for a type of item rather than your specific piece.

Both are useful but neither is a guarantee. The hammer price, and the total price paid with any buyer's premium, is what the market actually decided on a given day. For research, actual sold prices for closely matching items, in similar condition, usually tell you more than either an estimate or a guide.