Last month, when German Peter Hartmann’s two-year lease on his One Chatsworth apartment expired, the landlord told him his new rent would be $13,500 — a spike of 80 per cent. The sales director, who had been paying a rent of $7,500 a month for the District 10 five-room apartment, was shocked. “The reason they gave was that the market has changed. It seems to me that there is no legal limit,” said...