When I lived in Singapore landlords would often double the rent knowing you would have to leave, they then re-let at something between what you were paying and the double figure. By changing tenants they get their hands on a new deposit which they then use the difference between that and the old deposit, (which they will try and avoid repaying in full), to tart the place up, thus maintaining their obligations to maintain the property without having to dig too deep into their own pockets in one hit.
If you happen to know your landlord and get on with him it makes a big difference. Dealing through agents, who get a new commission if they get a new tenant at increased rent are no use to you at all, the best they might do is offer to find you somewhere else, from which they will also get a commission!