It's true, everyone can make a mistake sometimes. But: you yourselves set a guideline of a 1000€ installment. Even that would be suicide. The whole idea of buying a house in your situation... you came to that conclusion yourselves. How did that happen?
What I absolutely don't understand either are sellers like that. Either natural born assholes, or so alienated from themselves... a normal person wants to be able to look in the mirror in the morning.