How do you deal with pushback from increasing the rent?

[Sebastien Beauboeuf]

I've been looking at some small multi family homes on the MLS in Chicago and it seems like a lot of the rents on there are below market. I assume that the rents are placed by the seller's agent and are accurate. So I asked myself why are the rent low? Below are what I came up with.

1- the seller fully owns the property and doesn't really care about increasing rents

2- the seller doesn't keep up with the market and don't know he/she can increase rent

3- the seller is worried increasing rent might drive the tenants away

I figure investors like to see the low rent and have plans to increase it once they acquire the property. I always wondered how hard it was to do that? Let's say the tenants have lived there for years and always paid on time and kept the place in good condition. How does an investor come in and tell them they'll have to pay $200+ and risk loosing them and having the property(ies) vacant. How do they make that decision?