Oral contracts are usually binding in Germany if their existence can be proven in court. There are some exceptions, notably in the case of real property sales contracts. Normal wear and tear of a used item is not considered a defect. There is no automatic grace period during which an order to buy something may be cancelled. Under German marriage laws, a party can't file for divorce until he or she has been separated for one year, or for three years if the divorce is contested.
Annulments are very rare.
The differences between German and American laws are particularly obvious when it comes to contracts. In the US it is common, and usually necessary, to spell out everything in a contract. An agreement to rent an apartment or house for a fixed term cannot be terminated early except under extraordinary circumstances. A job transfer is usually not an extraordinary circumstance. It's advisable for Americans to have a German attorney lead them through this maze.