They take advantage of the fact that this is how the laborers exist. The laborers have competition with other laborers and the bourgeois profits off this competition. The laborers work for wages. Wages are the sum of money paid by the capitalist for a particular labor time or for a particular output of labor. In that sense, Marx said that the capitalists are buying the labor for money and the laborers sell their labor for money.
Labor power is considered the commodity.
The laborers exchange their commodity for the capitalist s commodity, money. Then the laborers use their received commodity to buy the capitalist s commodity to exist. The laborer s wages are just another name for the price of labor. The capitalists usually profit from these workers and if not that worker is gone form the production scene, the capitalist class. Unfortunately, the wages of the workers depend o the supply and demand of the product.