What is the agent’s incentive when selling her own home? Simple: to make the best deal possible. Presumably, this is also her incentive when selling your home; after all, her commission is based on the sale price. And so your incentive and the agent’s incentive would seem to be nicely aligned.

But commissions aren’t as simple as they seem. First of all, a 6 percent commission is typically split between the seller’s agent and the buyer’s. Each agent then kicks back half of her take to her agency. Which means that only 1.5 percent of the purchase price goes directly into your agent’s pocket.

So on the sale of your $300,000 house, her personal take of the $18,000 commission is $4,500. Still not bad, you say. But what if the house was worth more than $300,000? What if, with a little more effort and patience, she could have sold it for $310,000?

After the commission, that puts an additional $9,400 in your pocket. Yet the agent’s additional share – her personal 1.5 percent – is a mere $150. So maybe your incentives aren’t aligned after all. Is the agent willing to put out all that extra time and energy for just $150?

Suppose that Rick [the real estate agent] were to get 10% of the portion of the sale price above $300,000 instead of 2% of the whole price. Now a $25,000 difference in the sale price makes a $2500 difference in Rick’s commission. This more closely aligns Rick’s interests with Hanna’s [the homeowner] interests.

The big problem with this idea is that it supposes that all parties have a good idea of a fair sale price. With this type of commission structure, Rick is strongly incented to convince Hanna that her house is worth less, say $350,000, and that way the deal will give him 10% of the sale price above $280,000. If Rick then sells the house for $375,000, he gets a $9500 commission instead of $7500.