I've just been reading an article in the Ege Eye paper (english paper circulated in Kusadasi) about the tax dept in Turkey tightening up on people who rent out their porperty.
It seems that renting out a property comes under a tourism business activity law, which means that if you privately rent out your property in Turkey without using a registered Rental Agent (are they different from Estate Agents?) then it's possible that you're breaking the law.
The paper recommends that you should read
http://www.turkisheconomy.org.uk to keep up-to-date with current laws and regulations.
I've had a look at the website and it seems a great place to learn the rules for foreigners in Turkey. There's even a section on "How to form a company".
Alison