What pakeha has said. Some internet sites seem to specialise in selling film of which a portion will be outdated. If it's part of their business then the chances are that it has been stored correctly and selling "damaged" film won't be in their interest. I'd buy from such sellers even if the film is up to a year or maybe more out of date. If it is only a couple of months out of date then provided it hasn't been stored above a radiator or on the rear shelf of a car in summer, you are probably pretty safe with such film as well.