“I’m not anxious to have you own braces of Rembrandts, like any vulgar millionaire,” he wrote to her in 1900.

But the rapidly changing art market — characterized by soaring prices, high fees and a host of wealthy new buyers from Wall Street and abroad — has prompted scores of new players to jump into the pool, from young art-world arrivistes to former auction-house executives with an abundance of expertise and connections. “It’s the Wild West,” said Abigail Asher, who has been an adviser for 25 years. “It’s like being in a gold rush mining town. We have been the miners for years and a lot of people are just showing up now.”

Many of these advisers are changing the profession — aggressively pursuing trophy art, wielding greater power in negotiations and in some cases acting more like fast-moving dealers than high-minded consultants. It is not yet clear what effect the latest gyrations of the financial markets will have on the art market, but in good times one big sale can reap millions of dollars for an adviser.

Many veteran advisers view their new competition with concern. Some practitioners are too inexperienced to provide good counsel, they say, or use tactics that they warn threaten to sully the profession, like dealing on the side, or demanding broker’s fees from both their clients and the galleries that sell to them.

“There is a new breed,” said Wendy Cromwell, former president of the Association of Professional Art Advisors, “an independent contractor — kind of like black ops, like a hired gun — who can get you what you need in a tough, changing environment.”