Ill admit I have always found it strange to say someone committed an Averiah by eating something not permitted because of events not controllable by the consumer.
Simply if something had a Hecher and it turned out the supplier was dishonest and cheated, Its not your fault for eating the non-kosher items.
In todays society we do not control the food, We are not farmers, cattlemen or anything related to the production and distribution of food. Unless a person is willing to farm and raise animals you cannot control outside events. Obviosuly one should be dilligent (Meaning its wrong to go into a McDonalds for example) but if one goes to a frum store and buys an item with an acceptable Hashghcha, one can reasonable assume its kosher and if its not, the Averirah should be on the person who made the mistake , not the consumer