For the auction houses, once these consignments are secured — about four weeks before a sale, as the catalog is going to print — their focus shifts to potential buyers. Top collectors and art advisers receive (or have had) advance notice of lots they may like or an early look at the auction catalogs. “I’m continually on the phone to buyers, every day,” Mr. Rotter said. “As soon as I hear of something they want — I’d say: ‘There’s a great Frank Stella coming up. Get ready.’ ” As the auction nears, prospective buyers may be wined and dined.

Image Mr. Pylkkanen's auctioneer's hammer. Credit... Andrew Testa for The New York Times

Sometimes it goes much further. In late September, Mr. Shaw flew to the West Coast to deliver high-quality reproductions of works by Degas and Toulouse-Lautrec to a client who wanted to see how they would look in his home. To an Asian client, he is actually taking Modigliani’s “Portrait de Paulette Jourdain,” estimated at $25 million to $30 million. “We’ll hang it and light it and let him see it within his collection overnight,” he said.

In Asia, Ms. Wong — who can often be seen juggling two or three telephones at a sale — is alerting her clients to works they may like in the catalogs. “I will have had the text translated into Chinese first, so they will be able to read” it, she said. “Then the key is keeping them interested, especially in the week leading up to the auction. I give them daily reports. The key is to impart as much information as I am allowed, so they can make informed decisions.”

She is keen to provide price guidance. “The client may ask, ‘What do you really think?’ ” she said. “I say I think it will go for X. It’s important to have that conversation with the buyer as to why it’s worth more, so they are not caught out on the phone when they have only a few seconds to decide.”

Many collectors are perusing the catalogs on their own, of course. “I see what’s there that in one way or another, I want to be involved with — either for myself or if I want to aggressively advise a collector to buy it,” said Robert Mnuchin, a New York art dealer. If someone is interested, “we talk about prices, but nine times out of 10, the collector decides the number and frequently not until the moment of the sale itself.” Other collectors approach an auction with a ceiling on what they will bid.