What merchandise have you bought and then discovered it was worthless?
For me, it would be:
1. can opener (Dollar General)- I was so mad when I bought this and it did not work one bit. I got so mad at it and threw it in the garbage.
2. key chains (Dollar General)- NEVER buy key chains from this place because they always fall apart.
3. winter coats (JCPenney's)- Years ago I bought a coat and then the zipper fell right off. More recently, I bought another winter coat and the zipper fell off again!
4. cassette player (Family Dollar)- I bought one once and I played my cassette tape. When the tape was playing, it sounded like someone had just gotten shot. I bought a few more after this from this store, but never again because they all did the same thing.
Always check your labels and see where the stuff is made. If it is made in places like Brazil, Taiiwan, Indonesia, or some other unheard country, most likely it will be cheaply made. (No offense to the countries mentioned.)

What brand was the can opener? I'm not aware of any appliances being offered under the Dollar General brand. I think they sell Hamilton Beach can openers here but I'm not certain.

Dollar General does sell alot of cheap junk but you can find some good bargains in there. I prefer Big Lots and Dollar Tree though, Great place to find stuff to resale on eBay if you know what to look for

You could see if they have a return policy & take the items back if they do. I bought my husband a pack of underwear at the Dollar Store & they shrunk the first time I washed them.

That One Touch can opener--not only did it go through batteries like there was no tomorrow, it would often stop in the middle of opening a can!