How Can They Sell Great Products So Cheap When Their Expensive Elsewhere?

many of the items they sell are lower quality so that leads to lower prices. 

This is not true, not all items are lower quality, many items they sell are good quality however don't make it in the big marketing world. For example someone might have made there own lime of shampoo and conditioner however they couldn't compete with shampoos and conditioners with brands like Pantene or dove, so they sell there products to the dollar store to msimp pome sort of return rather than loosing there place on the shelf for good. However when it comes to food at the dollar store it is usually nearing its expiration date or already expired