I have heard the above statement aplenty times from agents. Let me give this example:
During hot hot property market days, speculators pay for the purchase option (not sales agreement) and put "TAN AH KOW AND/OR beneficiary" so that they can freely transfer the unit within the next 2 weeks = flip property for maybe just a 1% downpayment.
Appointing an exclusive agent is like giving others a chance to flip your property for FREE. You don't even get a 1% downpayment. It is like you granted them a "free option to purchase on your house" for 2-3 months but they don't promise any compensation, for failure to do so. Being exclusive, they will still take commission in the agreed period (2-3 months) even if a transaction is closed without any effort or contribution from them.
This is why exclusive agents are not in the best of your interests. Of course, if you sell if yourself, I still encourage you to reimburse agents who can bring you prospective buyers 0.5 - 1% commission.
here's an earlier take on exclusive agents:
I assure you that you will never get the best price for your unit when you appoint an exclusive agent. Exclusive agents can promise you the sun and the moon but once you appointed them as your exclusive agent, the game is half-won for them. In short, they have no incentive to protect your interests going forward. Always declare the sale of your unit, free-for-all / open for all agents. In this way, all the agents will have equal incentive to convince the buyers to offer a higher price, as much as they want you to lower selling price. In addition, you will get maximum exposure because you can get more agents to promote you unit online or in classified ads which will translate to greater buying interests.