When is it legal for a real estate licensee to boycott competitors?

Answer 1

If a Realtor is an independent, they do not have to show homes of ANY of their competitors. And the competitors do not have to show homes of the independent. This would be self defeating as the independent would only have a few homes to show and sell vs the hundreds of thousands that get listed by all the various agencies. Usually the agencies have agreements to show each others homes and if a sale occurs, they split the amount earned in the sale.

Now, if one agent only shows the homes he personally has listed and never shows homes of other agents, that is not a crime but it is a contract violation. He can be sued for that.
Sometimes you will catch an agent showing HIS homes first, then the homes listed by HIS agency and only after that will he show the homes of other agencies.

Best approach is to do your own search so you know what is available before you talk to an agent. A good website is listed below.

Answer 2

That depends on what you mean by 'boycott competitors'. If you mean refusing to show clients homes listed by other Realtors or refusing to other Realtors to show homes you have listed, I doubt it is ever legal. Even if it is, its a good way to kill your own business, and unlikely to damage the competitors.