If you didn't pay commissions sales people would start coasting once they made their numbers. Imagine you have to make a million on sales per quarter, and three weeks in you strike gold in the form of a $1.1m contract.

Sure, you get bonuses for exceeding your numbers, but you could spend the next two months slacking off, which would probably be worth the lost income.

Worse, from the company's perspective, you might try to make sure your new prospects don't close until next quarter, just as a little bit of insurance in case it turns out to be leaner than this one. You're already drinking the coffee - what's the rush?

Sales is a tough job. It's a lot of travel, a lot of rejection, and a lot of stress. If I had to do sales you can be damn sure I would expect a lot of compensation.