I can not speak for other dollar stores but please let me educate you on how Dollar Tree manages their corporate chain.
First off there should never be an expired item in the store. If by chance you happen to come across an expired item, by making an employee or manager aware the item will be removed from the shelves immediately.
Secondly if you look closely at many of the products in the store you will find brand names to be different but the manufactures to be fairly well known. Americans tend to buy known brand names, thanks to advertising. Ask anyone who works in a packaging and labeling factory and they will tell you they label the same product with multiple different branding labels.
With that said my final point. Many company's have to much product, Dollar Tree corporate finds these companies and offers to buy all of their over head that would otherwise go spoiled or unsold at less than 48 cents on the unit. A prime example is Chicken of the Sea tuna which is owned by Van Camp's, however in Dollar Tree it is simply labeled Van Camp's (same great tuna just a different label and 20 cents cheaper).
Items will only be thrown in the dumpster if they're damaged or expired. Otherwise they're sent to another branch location for sale if it doesn't sell well.
Sure Dollar Tree deals with mass production companies located in china and other "cheap labor" parts of the world, so does the rest of the big boys in the S&P 500.
In my community Dollar Tree is the only company that hasn't frozen wages, still offers competitive wages, and offers decent employee benefits. I do not work for Dollar Tree nor am I affiliated with them in anyway, I currently work for the black hole A&P.