I've worked in retail quite a bit, and there is one ulterior motive behind the approaches a lot of people don't realize.
Theft prevention!
It's a proven fact that simply making the staff's presence known reduces theft. Shoplifting is a HUGE problem in retail. Many companies train their employees to approach every customer, and ask if they need help. Customers who are approached are less likely to steal anything, even if the employee is told, "No thank you, I'm just looking."
Often the customer doesn't know where to find what they are looking for. Often they are on a "mission" to get the one thing they came in for, and get out. When you act as if you are annoyed, they move on looking for customers that do want help. So when you get to the register and there's no one there, that's why. They're helping people who wanted the help, and very likely following them to the register with the item they want to purchase.
There are some companies that take it to extremes though. I used to work for Sears, and I can tell you we got complaints from customers all the time about being approached eight to twelve times by the time they'd made it my department. This is because Sears, at the time I worked there, had an idiotic policy that REQUIRED every employee (even if they weren't in sales) to approach every customer. And if we didn't, and a manager noticed it, we were chastised and even disciplined for it. Add to that that the sales people made their living on commissions, and there was a virtual war on the floor for the sales force to get to customers before anyone else did. It was stupid, and did nothing but promote some really childish behavior, and did not go unnoticed by many of the customers.
There is the other extreme too though. Ever been in a store where none of the employees EVER make eye contact, and actually AVOID YOU instead? Let me tell you, when you can't find what you're looking for, that, to me, is even MORE annoying!
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...