Faced with a high minimum wage, shop owners would be sure to look for ways of keeping costs down by firing people, or by squeezing differentials as far as they dare.
Regulators cracked down on some specialists two years ago, accusing them of improperly stepping ahead of client orders and benefiting by minor price differentials.
Germany's system of centralised pay bargaining, under which unions and bosses set wages and hours across whole industries, makes matters worse by compressing wage differentials.