The booksellers in the room (virtual or otherwise) are, by definition, competitors. This means that under the law, they are prohibited from discussing certain things.
There can be no discussions of price or pricing policies. Competitors are never allowed to agree on the price at which merchandise is sold, or discounts at which merchandise is offered. All discussions of price and pricing policies are strictly off-limits.
There can be no discussion of boycotts. Competitors cannot agree to cease doing business with any supplier for any reason. Nor can competitors agree to urge consumers to boycott a third competitor. It’s collusion, and is strictly prohibited.
There can be no discussion of dividing up a market. For example, if there are two booksellers in New York City, they cannot agree that one will market only to consumers north of 57th Street while the other markets only to customers south of 57th street. This is also collusion and is prohibited.
All three of these prohibitions come to us via the Sherman Antitrust Act, which carries treble damages and jail time. All three are per se violations, which means it only has to be proved that you engaged in the activity—whether or not there was intent to harm, or actual harm caused—for you to be guilty of violating the law.