Isn't this a bit circular though? If the fees are high enough, it allows for an oversupply of realtors ... which only gets worse in a rising market because fees are % based and entry-to-market (for a realtor) is fairly easy. NB: easy to enter doesn't mean easy to succeed, which is borne out by the longevity statistics, I believe.

Sure, but a real estate agent who has a "seller" client has a pretty easy time finding "buyer" clients -- run an open house on a property you're selling and prospective buyers (specifically the ones that decide they don't want to buy the property being shown) come to you without even knowing that you exist.

Really, really depends on the specific house.