The pay structure for real estate agents creates a misalignment of their own interests and the interests of their clients -- the actual buyers or sellers of homes. Real estate agents get commissions on homes they sell, encouraging them to hike their pay by pushing the most expensive houses on their clients rather than helping them find the best fit for their needs and budget.
But if the selling agents want to sell the most expensive houses, this should be good for home sellers, right? Nope. To maximize their pay, real estate agents also have to worry about volume -- that is, they want to speed up the sales process to increase their own pay per hour. This means that an unethical agent could stoop to selling houses for less than they are worth if it means getting a quick commission and moving on to the next house on the block.
Car salesmen get a bad rep for similar reasons. Like real estate agents, they get commissions on the cars they sell. This not only encourages them to push the most expensive cars on their clients, but to also trick customers into buying a bunch of unnecessary add-ons.