I've had generally good aftersales service from Carrefour. However their pricing system is bad, frequently the price charged does not match the shelf price and you have to be very diligent when the cashier is scanning the goods- you really need to know the prices of things.
One of the worst things at Carrefour is the quality of fruits and vegetables- a lot of the time it's okay but sometimes the produce looks like it's only fit for the garbage dump.