On two or three occasions I've had to return an item to Aldi and, providing I still have the receipt, I get an immediate refund.
Last Sunday I bought one of the £6.99 aerial amplifiers which didn't seem to be working properly, so I took it back and exchanged it.
I had to do this three more times before I got one that was "working".
Turned out that it was my (easily made) mistake and felt a bit sheepish afterwards, but there was never a quibble with the Aldi staff about swapping the product so many times.
They did state that I was the only person who had had problems...:-)