I just wanted to add a post to say that I was supported in a discussion with the taxman by my property manager (Olga at Interturk Estates). I rent out occasionally through the year - often to family/friends but somtimes to people who have found my site via CalisVilla. I had heard from a good number of the people visiting that "the Tax Man" had come on site and was asking them for the days they were staying, how much they were paying etc. For this reason alone, it seemed important to get to the tax office and find out what I needed to do to be registered.
As I speak very, very limited Turkish, I had no hope of doing this on my own. Olga was kind enough to take me to meet with the appropriate person and they recorded my (and my apartment) details. Now, when a visitor rents the apartment, Olga arranges for them to sign a simple one-page statement (booking form) confirming the dates they are staying and the amount they are paying. This gets off-set against the bills/maintenance paid throughout the year as well as a certain amount that can be earned before tax is payable. At the end of the year, if I do owe any money at all, this will be paid and all is above board.
I feel much happier knowing that I am now "above board" and that my guests will not get hassled whilst they are on holiday.
Clearly - it is entirely up to you as to if/how you manage this, but I am pleased I have got this sorted.
Good luck to all who are in similar situation.
Debbie :-)