Normal practice when renting
The general terms for an apartment rental in Germany are these:

You pay a three months deposit and you are given a clean, newly decorated apartment to move in to.

At the end of your rental, you give your landlord three months notice of departure and you leave a clean, newly decorated apartment.

Read that last bit again, you are supposed to paint it and stuff before you leave! You are also supposed to know a long way in advance that you will go.

If you do not redecorate, you stand to lose your deposit. If you give one months notice, you stand to lose two thirds of your deposit.

Often, there will be fixtures and fittings that have been installed by the previous tenant. You may be expected to pay the tenant for these as part of the moving in process. This can be expensive if, for example, you are asked to pay ten thousand marks for a luxury fitted kitchen. You can read more about these items below:

Germany Living in Germany
Countries Notes about some other countries
Home See what else is on this site
Apartments The main apartments page
Your money Deposits and Notice Periods
Your responsibilities Redecoration, Fixtures and Fittings