I'm not sure of the 'correct' answer, but I would think if its from a reputable place it would be ok - but maybe just stay away from the raw fish ones.

Otherwise - have you thought about making it yourself. I make it myself (did some last week), that way I know its fresh and whats in it. You can get kits from the supermarket and they are rather easy to do (I think so anyway and I'm not the best in the kitchen either). I usually do avocado ones, marinated BBQ chicken in teriyaki sauce and a couple of sweet chili tuna ones - then usually eat them within 24 hours (along with DH's help )