The Apple Store in St Davids 2 in Cardiff is main store in the capital. I'm yet to have a problem with them, but it could be the person the OP got that made a mistake etc. It may be flagged on their system now too in case the device is taken elsewhere.Some stores in more seedy parts of towns are less forgiving than ones in more upscale places.
https://www.apple.com/uk/retail/stdavids2/