They claim that they match in-store prices: https://support.google.com/shoppingexpress/answer/4559805?hl...
Essentially, you're paying them to go to the store and pick up the item for you.
Re:Google Shopping Express
by superchink on Tuesday July 15, 2014 @06:34PM
(#8039531)
As others state, they do not seem to mark up. In fact, sometimes prices are adjusted after placing the order to reflect a discount.
I've never seen them mark anything up. Sale prices are reflected as well. They must be losing money on each order currently.
I did a quick comparison between a random product: LG 42" Class 1080p 60Hz LED HDTV. Target's direct online store offers the TV for $379, while Google Shopping has it listed for $449.99. I haven't done other comparisons, but this seems to confirm my belief that Google is marking the products up to some extent.