As a landlord, I usually raise rents by 3-5% per year. Any more than that here will cause most people to move to another location. A smart landlord will not try to raise the rent by too much unless the market rent in the area is about 20-30% higher than what they are charging.
As a landlord, it’s better to keep a tenant rather than try to squeeze every dime out of him/her. It usually costs about $2000-$3000 to advertise and prepare a unit for a new tenant. Certainly if I was a tenant, I would negotiate any rent raises down by noting that fact.
I wouldn’t worry too much about rents. It is highly dependent on salaries, yes, and of course subject to demand and supply, but the pure fact about it is that most landlords are desparate to keep their unit leased and most landlords undercut each other all the time. In terms of economics, rents are a pretty efficient system.