The good:
=> excellent location (near some of Berlin's greatest parks: Viktoriapark, Park am Gleisdreieck, Tempelhof; near Bergmanstraße with many excellent shops and restaurants; Kreuzberg in general is one of the best places to stay; relatively close to U-Bahn)
=> sharp price for the time of year
=> very clean
=> quiet street and building
=> hottest day of the year (39°C) but the apartment was cool enough to sleep
=> very easy check-in with good instructions
=> small, but more than enough space if you're just travelling
=> tv with Netflix (but... see below)
The bad:
=> Really atrocious wifi which is something that has been mentioned by other guests and I do not agree at all with the host just explaining it away. They have to invest in better internet - period.
I averaged between 2 and 15 mbit/sec on speedtest on multiple devices and ended up using my mobile data because that was faster. Those speeds are not even considered broadband according to some definitions (FCC for example) and are therefore completely unacceptable in 2022. Even the 25 mbit that the host would consider acceptable in earlier comments is just him prioritising profit above guest comfort.
tl;dr: If you value high and stable internet speeds (for work for example) and do not want to be thrown back in time, this is not the place for you.
=> Netflix on the tv kept bugging out from time to time due to loss of internet connection (I looked up the error codes) or reverted to a resolution where you could count the pixels.
=> If you ask your guests to sort the trash then you should provide them with decent trash cans to do so. Mentioning in the apartment guide that you will do that some time in the future is just lazy. Go to the shop, buy a trash can system with sorting and put it in the kitchen.
=> No check-up from the host during the stay (most Airbnb's do this as a matter of being polite); just a message asking for a 5-star review.
=> The apartment could use some love: no decorations, no extra wall sockets so you can either use the bedlight or charge your phone (not both), loose cables coming from the electricity box in the hallway, the cabinet in the bathroom feels more like something to put under your desk than something you would put in a bathroom - and it was not clean at all (compared to the rest which was very good); the welcome booklet had a dirty feeling to it (the information in it was very good, however).
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Although I would recommend the apartment to someone who just needs a place to stay while city-tripping I cannot in good conscience rate it very highly.
The remarks above really make the place just feel like an average 3-star hotel room instead of a home or part of a home, which is what often makes the Airbnb experience better than a typical hotel experience. That is why I will be rating this three stars. With some effort from the owners I could easily give them a 4-star rating but doing that now would be asking too much.