In the former case, you can sign a sales contract with the seller and notarize it. You can also deduct a small sum of money and give it to him after the transfer of property rights. (Note: There are certain risks, and this kind of second-hand house notarization belongs to the second-class protection of national laws).
If it is the latter, the house price should be very cheap. The price of this kind of house is generally nearly half cheaper than that of commercial housing, so you don't want others to give you less, so you think you have made a profit. The sale of this kind of house is still notarized.
The two notaries here mainly show the landlord how much you have paid, and then you can sign the sales contract, how much you can claim for breach of contract and so on.
I suggest you change your house. Do you mean that the property right belongs to the unit? You can ask him to show you the real estate license. Note that if the real estate license is issued by the state, it is a big property right, and nothing else is. The house you are talking about may be a small property right and a working house, and the purchase risk is greater.