Want to drive more online sales? Here's what you need to know about what really makes people buy.

The average shopper can't remember a time when fixed prices weren't the norm. After all, it's been well over a century since rounds of haggling was the way goods and services changed hands. Fixed prices were introduced in the early 1800s as an attractive new feature that could save consumers time, money, and emotional energy, and were a great benefit to merchants, too.

The benefits stuck, even in an era of e-commerce when consumers assume online stores offer lower prices without brick and mortar overhead and when comparison shopping is easier than ever.

However, a new startup called PriceWaiter is bringing haggling back to e-commerce, and it's bringing a refreshingly human element to the online marketplace. The approach also highlights three behavioral economics concepts that play a big role in selling goods online: