Duplex have different zoning that may permit additional units.

(if the buyer wants a more solid commitment)Once a buyer has spent money they are somewhat vested in buying the property and that gives additional negotiating power to the seller.

Is the portal that the landlord and tenants use an additional charge?

In addition, when you have leverage you have the other benefits which @Ali Boone mention.

I heard that less than 20% down causes additional insurance fee? 

Foreign nationals have the same rights to purchase real estate as German citizens, making it easy for Americans to invest in the German market without additional legal barriers.Furthermore, Germany has a transparent legal process for buying property, ensuring clarity and security throughout the transaction.

Additionally, be sure to have an accurate ledger and your signed lease agreement.

They forget time is money and the PMC shouldn't be expected to do this without additional compensation.Also, many owners are too focused on the cheapest price without understanding all the potential pitfalls. 

Let me know if you need any additional information, feel free to give me a call. 

Not a big fan of LTR furnished units, the additional wear and tear isnt worth it in my market and of course smoke smell can be hard to get out.