Not discounting your experience but I've bought protein powder and flax oil from them for about 4-5 years and have never had a problem. Good prices too. So they don't always suck.
Remember that just because an item has a date on it does not mean it's no good. Like milk from the store, it has a date that may mean "sell by" the milk itself will probably last a good week after that. It doesn't go bad on that date. Now I don't know specifically about the stability of dextrose but if it's powder wouldn't it last years?
I do think they should have handled it better and 10 months is a long time.