I purchase photography equipment. Any photographer will tell you that photo stuff is expensive (my camera body alone cost $3200!). Lenses are ridiculously priced as well.
I love to order online. It's fast and convienent and, if the shipping charges don't offset it too much, quite often cost effective. However, when the dollar amount starts cranking up, I'm still more comfortable talking to a human. That is an emotional thing and not based on any sort of logic. However, there is a logical bonus that does come with humans!
Computers don't work off of comission. Humans do. A computer won't cut you a deal to ensure a sale. You might find some application that will automatically adjust its price to be even with, or slightly less than, a competitor, but there's nothing like a salesperson simply quoting you a price lower than you were expecting to pay because he or she wants the sale. A computer doesn't lose sleep over a customer leaving without purchasing.
Another benefit of humans is that they are quicker to offer alternatives to purchases. When an item is sold out, a salesperson can find a comparable price and or product automatically. Also, since many salespeople understand the products they sell, their biases can often help (i.e. 'Oh, well you could get the R2 droid instead, but I've found that their motivator units aren't that great').
So, there's still an advantage to human beings. I'm sure in time someone will make a computer system that can haggle, but until then, I still plan on dialing up when the receipt is high.