Bob,
I have 20+ years working with/alongside Dominicans. Look at this from a different perspective.
Like most local grocery stores, young people are working there in most positions. It's great to see kids that have the work ethic to get out and make some money legitimately, no?
I'm confident they don't go through a training class at Playero on how to cheat customers. And... they really don't have evil intent to defraud you.
These kids have likely seldom seen an example of good customer service in their lives. They deal with Orange, Claro, local pharmacies, etc, etc. They're for the most part not the best educated, and probably making about 6000-8000 pesos a month. They work all month for what you or I will drop in cash on a few day's groceries.
Yes, Playero could train them better. However, speaking from experience, it at times can be like herding cats to try to keep employees here focused in spite of training efforts.
These people work hard. They stay busy at that store. The registers are always running, the bag boys are always busy. The stock clerks keep the shelves well stocked, there's ample well-organized parking, and the store is clean. Sure, they're not up to first world customer service standards. But overall they do a damm good job if you ask me... and certainly better than any store in the immediate area.
Anyone venting their frustrations at the 17 or 18 year old clerk at the register and walking away without purchasing anything is teaching no one a lesson other than that some gringos get pizzed easily. Always better to take such an issue to the owners, especially when you can at Playero. Unlike having no ultimate power to appeal to at Orange, La Sirena, etc, etc.