[leghifla]

Usually, the more competition there is in a market segment, the lesser the margin becomes.

Let's say your customer often "complement" your offer A with B from another company. If the other company faces fierce competition on the market for B, its margin will be low. So, you may be able to capture a little bit more of the customer's money: he wants to spend x on both stuff, the less it spends on B, the more it can spend on A.