... can I have problems as a seller?
The biggest risk that a seller of an apartment faces is not receiving money from the buyer after the deal is closed. However, in the case of a mortgage, this is practically impossible for a number of reasons:
the transaction is strictly controlled by the bank, and in most cases the bank will transfer money to the seller;
when depositing money in a cell or transferring it to a special current account, it will already de facto belong to the seller, it remains only to confirm the fact of the transfer of ownership;
in case of non-payment, the agreement may be challenged in court and declared null and void in accordance with the current legislation, and the seller will be able to take the apartment back.
The risk that the seller gets counterfeit funds is as unlikely as the one mentioned above. If the money is transferred by a bank, it will be genuine by default. Even if you transfer part of the funds in cash, you can always check them right there in the bank using a special machine.
Another risk, which is more real, is that the bank did not approve the deal. There are many reasons for this. In this case, the seller risks only the fact that he will have to return the deposit, since the deal was broken due to the fault of third parties, and not on the initiative of the buyer. The demand to return the deposit in double amount is illegal, since the seller did not refuse his part of the agreement. Therefore, it is better not to spend the funds transferred to the seller as collateral.