As you can see, typically the seller pays, but the seller pays the commission from the proceeds of the sale. So, typically, the commissions are built into the price of the home. Since this is a long standing and accepted practice, the market value of homes (in general) reflect this.
Phil's answer here alludes to this fact.
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There's no rule or law regarding how much the commission rate is or what the split should be. The typical range for a residential commission tends to be between 5-6% though occasionally it's more and occasionally less.
For those selling on their own, they should be prepared to offer a buyer's broker a commission in the range of 3% if they bring about a sale.
Hope this helps.
When renting real estate with a real estate agent it's even more ambiguous. Here in New Jersey it is not uncommon for the tenant to be required to pay the entire real estate fee. However, just as with sales, everything is negotiable and tenants can propose that the land lord pay the fee, or that the fee be split between the landlord and the tenant. I always tell the landlords I work with, 'pay the fee and you will be on the top of everybody's list', but in a corporate relocation situation the relocation company tends to reimburse tenants for the fee so it's far more common to ask the tenant to pay the fee and then negotiate.