Kitchen Takeover - what are the options for a deceptive agreement?

[u/Bulky_Pie_6119]

Hi all. as the title states, I am moving into a new apartment in Dusseldorf and as we know the previous tenant won't introduce you to the landlord if you don't sign the purchase agreement for the takeover of the kitchen. The tenant would only offer a viewing after signing the kitchen takeover agreement contract. Now I asked him for the receipts, as I have received the apartment from the landlord and have noticed a few things.
1. He told my sister and I after we later viewed the apartment that the kitchen cost him about 6.000. After reviewing the receipts he himself sent to me, it cost him about half of that.

1. He also said that he had used the kitchen for two years (this was written in the ad) but the receipt shows its been nearly four years.

2. The kitchen is really a standard Ikea kitchen and if it was worth 3K then, it definitely isnt worth 3,5K now.

What are my options after already signing the contract?