Open Agent or exclusive agent

[Peter Sik]

Asked 2 agents, they said you have to have exclusive listing agent, and there is no such open agent. 

According to what I found:

"What does open Agent mean?When the listing is open, the agent who makes the sale is paid the commission, not the listing agent.
If the homeowner finds a buyer without the assistance of an agent, no
one is paid a commission. If the agent has an exclusive right to sell,
the agent earns a commission regardless of who sells the property."

That is not true.

I would like to know:

1. Why they don't know or not willing to tell there is an open agent?

2. Does it really that much work and spending to list a property?   

3. What is the pro and con for exclusive and open agent on this marketing situation now?