Yes. Any experienced, reputable Broker will insist on an exclusive listing agreement before agreeing to the responsibilities of selling a business. Brokers invest a great deal of time, effort, and marketing dollars upfront to prepare a business for sale (usually at zero cost to the Seller) in exchange for the opportunity to earn a commission.
Employing several Brokers to sell your business may seem like a good idea, but it usually backfires. The same business gets marketed differently, often using different financials or asking prices, causing confusion in the marketplace. Buyers see conflicting ads for the same business, become confused or suspicious, and quickly lose interest.
Consistent, professional, experienced marketing from one source is the fastest way to sell a business. Remember that it takes time, even for experienced Brokers!