My 2 cents on this question:
Yes an Owner can sell their property without going thru a property agency or RENs. This is a free trade country, and there is no law that mentioned you must go thru a property agency to sell or purchase your property.
The question to the owner is that whether they want to go thru the hassle of initiating the all rounded process or not.
Secondly yes there are scenario whereby:
1. Agent bring the buyer to the owner property, and happened that owner is still staying there, and at the end of the day owner is dealing directly with the buyer (very rare case but it is still happening, as the owner wanted to save the professional fee that they are paying to the agency)
2. Another case would be Brokers (so call runners that is brooking the deal with the owner but is not a genuine real estate negotiator) that often tarnish the reputation of an actual Real Estate Negotiator. They represent themselves as real estate negotiators but they are not attached to any realtor and working on their own. People often mistaken brokers as bad agents (but in real fact, they are not agent in anyway)