$50K is too much for a deposit
Pre-approval is not approval. In a nutshell, the lender will lend you X amount based on what you TOLD them you earn and have as equity. When it comes to actually lending you the money the bank then does all the checks to make sure you are not bullshitting.
Anything bought on finance is effectively a "cooling off" period, you could always arrange finance to fall through if you happen to change your mind....
That's why sellers prefer cash buyers...no finance ...front up the cash and straight to settlement.

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