haven't read all of the responses, but as the first responder said, the landlord can do whatever he likes until you've signed the actual lease.
last year, we had not only agreed on the rental and conditions of a place, but i had signed the prelim, handed over 1.5 month's worth of deposit and my financials, only to get a call the next day from the agent apologising... he said that after seeing my financials, they decided they wanted +12.5%/month than agreed. we just couldn't manage that, so got our money back.
incidentally, we drove past the place about 6 weeks ago... it's still empty! the idiot lost out of our paying a year's rent because he got greedy and wanted another $5k/month!