incrediBILL - 6:16 am on Aug 8, 2012 (gmt 0)

But a normal visitor looking for products always puts something in the cart and then checks shipping prices. These visitors never put anything in the cart. They just hit and run.

I shop a lot and rarely put things in carts so you really can't judge by that activity. As a matter of fact, I used to write ecommerce software for about 10 years and the demographics from most stores I've seen show more visitors not putting things in carts than those that do, but it also depends on the store as well.

You might want to check the source of your traffic because different referrers can explain the variation in traffic behavior.