yeah we have all had this problem before. before fixing i have explained to customer that they are bowed and will show shadows on the grout line, on most occasions the customer has agreed to change the method of fixing, however on a couple of occasions the customer has not adhered to the advice given and then been slightly surprised with the end product. nowadays my first instinct is to give the customer other options rather than brick style
i do believe the tiler should have pointed this out to customer prior to starting or when he first noticed, but remember we only get oneside of the story on here
some pics would be handy in order to see the quality of work,