How do you confirm you are charging the correct rent for your apartments?

Hmmmm...Tough question. You just have to know your market. Get to know some of the other agents that do leasing and talk with them. Same thing with investors, property managers, or anyone else involved in leasing.

In my area, very little leasing activity goes thru MLS so it's mostly word of mouth. This is where your networking skills can really come into play for you.

You can always call around and act like you are a prospective tenant and get pricing to compare yours to. Take into consideraton, if you have a good paying, problem free tenant it's worth it to not raise the rent unless necessary. They are hard to find.

I'm an agent, so I run a list from MLS. If I were not, I'd scan the paper, run some sign calls, and ask a couple of agents with for sale signs in the area. The general rule I have as an agent is I will share information and spend a little time with you if I think the other person will consider me in the future with their real estate needs. You are a potential client with rental properties that might want to buy more or sell some one day, or even put your stuff into property management. I would consider yourself qualified to attract an agent's attention. I love having contacts like this.

I don't like to over rent. I would rather take less and get it that take more and collect it in court.

I agree with mWoods here. If you cannot find any rental "asking price" data on Craigslist or Rentals.com, simply just call around acting as a prospective tenant to learn about rent prices in the area. Very nice!