"I will take a look at everything on the shopping list," said Goldstein.
Goldstein's ritual has been dubbed the "scan and scram" or "showrooming," and it's changing the retail landscape.
Shoppers are virtually price checking TVs, appliances, clothes and even wedding rings. One online jewelry store, which says it offers the same rings major retail chains do for less, was actually surprised to see that 8 percent of its customers purchased their new bling through their phones.
"As soon as they find the deal they want they're ready to jump on it because they've been educated, they're fully aware of what's out there and what they want," said online jeweler Vipul Lakhi.
How many customers are scanning and scramming? One study found that 25 percent of adult cellphone owners used their phones in a store to see where they could buy an item for less. And 5 percent of those mobile price matchers bought the item online. Amazon and eBay even launched price comparison apps to make it easier for shoppers.
But some traditional retail stores are fighting back through a number of tactics. For example, Target offers exclusive products you can't buy anywhere else. Nordstrom offers free shipping if you buy something in-store or online. Macy's and Old Navy send in-store only coupons, while Sears stresses immediate gratification.
"You can actually get the product the same day you purchase it. No waiting for something to ship to your house, no paying extra shipping charges to get it expedited," said Don Perkins with Sears.
But they'll have to try harder to convince showrooming shopper Goldstein to stop.
"In the big picture you can save a lot of money," he said.
Some stores will offer to match the prices of online retailers, so it may be worth asking the store manager if they'll give you the same price.