What the actual sales agent gets paid is based on an agreement with the brokerage. What you owe to the brokerage is based on your contract/listing agreement with them. What does your listing agreement/contract say? I am positive it addresses commission.

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You are probably referring to an ad that says if I cannot sell your home, I'll buy it?

You are hiring a Realtor to sell your home. So if you pre=agrree on a price that if it does not sell, they'll buy it, they are still conducting a transaction. So in most cases you will pay a commission. This is a business, not a charity. We would still have to do the work. BTW this does not occur very often.,