Incredibly easy to do at any store
The first key to pulling this off is realizing that most store staff rarely, if ever, care to know who their customers and vendors are, and cannot identify who may be trying to compromise their systems. I work as a freelance merchandiser and auditor for several different companies. Often times I work for these separate companies at the same store within days of each other. The store staff rarely, if ever, recognize me, even though I live three miles from the store and shop there a few times a week.
The second key is to look like you know what you're doing. When I was working for a company that needed to advertise a big event but didn't have the budget to do so, I once went to every newspaper box and news stand in three towns slipping an advertisement into the daily newspaper. This would have cost thousands of dollars to do if they had paid the newspaper. Instead I spent $20 in quarters to access the news boxes, and nothing to go into stores and news stands to insert the advertisements in the early morning hours, just moments after the newspaper carriers delivered them. If anybody asked me what I'm doing, I told them that the newspaper forgot to include a huge advertisement for a client and I had to go back behind them and fix them. Nobody ever questioned me, nobody ever asked me for ID, nobody ever called the newspaper to verify it.
The third thing is to actually appear to be who you are. When I am a merchandiser, I always wear a nice short-sleeve button-down shirt, a tie, and clip-on name badge etc. I look like I'm representing the client, I go to the front desk and I sign into the vendor log (and often get a peek at what other vendors are coming in and out of the store, at what hours, and how often). When I was impersonating the newspaper carrier, I dressed and acted the part - warm clothing that was slightly worn so I looked like I didn't care if I got news ink on them, slightly rotten attitude because I'm up so early in the morning working, etc.
So I could see these scammers easily working this over. All they would have to do is look like a hardware tech, show up at the store, sign into the vendor log and get to work. If anybody questioned them, they just explain that they're from XYZ company and are here to do upgrades on equipment, convince staff it will only take a few minutes, and then get right to work. Name badges, company cards, even a faked letter of authorization in case some real hard-ass manager questioned anything. I'm sure in nearly every case, few people if any questioned what was going on. Because one assumed the role and demonstrated they knew what they were doing, store staff blindly trusted them. And, in truth, most likely the store staff was either too busy working to notice, or too busy goofing off to care.