This commentary originally appeared on Real Money Pro at 10:00 on June 23. Click here to learn about this dynamic market information service for active traders.

Online shopping in general, and Amazon (AMZN) in particular, has changed consumer behavior forever. Malls will never be the same, and some old-line retailers, like Sears Holdings (SHLD) , might not survive the changes.

Amazon's foray into food shopping is taking center stage. The reaction to last week's announced purchase of Whole Foods Market (WFM) has been startling. Take Costco (COST) , for example; this stock has dropped from $180 to $160 over the past week.

Costco is being hammered on the legitimate concern that shoppers will soon have the ability to place Whole Foods grocery orders via Amazon. If Amazon can deliver the goods quickly and cheaply, that service could be a huge winner.

However, I believe the punishment that Costco has taken over the past week has been overdone. First of all, it could be a long time before Amazon offers a cohesive Whole Foods delivery service. By the time that happens, Costco could have a similar service in place.

Beyond that, Costco and Whole Foods are dissimilar in many ways. In addition to food, customers can purchase furniture, electronics and automotive supplies at Costco. Meanwhile, Whole Foods is a specialty organic food store in a time when organic food offerings are becoming ubiquitous.

Technically, it's nearly time to buy Costco. The stock is approaching its 200-day moving average (blue) for the first time this year. That moving average is currently located at $157.35, which would make an interesting entry point for longs.

Costco is also oversold for the first time this year, according to its RSI (relative strength index) indicator (shaded yellow). A buy signal will occur when that indicator rises above 30 from its current reading of 23.65 (green).

Chart source: TradeStation

There is one huge reason why Amazon won't be able to roll over the supermarket industry quite as easily as it did the shopping mall: There will be no element of surprise. Amazon's dismantling of the shopping mall is the biggest story in retail, and one of the biggest stories in all of finance. It has repercussions that stretch far beyond the financial markets.

Five years ago, even if you had the foresight, you may have had difficulty convincing the officers of major mall-based retailers of the enormity of the Amazon threat. Rest assured, that will not happen with Costco or its competitors. Amazon has gained much over the years, but if there is one thing that it has lost, it is the ability to sneak up on its competitors.