I think most of the dollar stores carry stock that would not sell at other full price retail stores, or stores that were closing for what-ever reason.
Lots of their basic stock is not name-brand like these paints are, and is specifically targeted to be sold in these stores. Usually their quality is low end, and possibly less quantity than what you are used to buying.
I would not hesitate to pick up a few of these name brand cans and give it a try.
When I buy a rattle can, I always shake it in the store and make sure that the mixing marble will still make noise. When I get home, I store the cans upside down for a few days, and shake them up whenever I think about it. Some of them sit on the shelf for a long time in the retail stores.
