Legally ambivalent
Typical predatory company, but atypically aggressive about it trying every possible way to get money out of tenants. Which they know full well are desperate, Berlin being Berlin.
Anecdote time~
The heat went out for all of December. The landlord took their time sending someone out. I honestly didn't notice it as I am made out of ice, but the others were literally getting sick because of the cold. It was I think -20 at one point. So the heat finally gets fixed, I again don't notice but everyone else does, and we all get an email. This company is graciously offering a 5% reduced rent because the heat was out.
The law is clear---during the winter months if the heat fails it constitutes a total deduction of rent. I tell them that, quote the law referenced, and withhold what was entitled. They email a few times threatening me with the contract, claiming that it was a different month that I didn't pay for and I was going to be evicted if I don't pay, but eventually that stopped and nothing else happened
As for the others, they paid the lowered amount (one withheld 15% to his slight credit), and in doing so were locked into konkludente Zustimmung-implied agreement-that the withholding would be 5%. This means that they can't withhold in later months and the company essentially just salvaged from them 95% of their rent which is legally forfeit. To be clear, the email didn't make it seem like it was optional and the others therefore did not seem to realize that it was.
A few months later we have an exodus because one of the roomates was essentially driving the rest of us out with his loud rude behaviour (which the company did nothing about despite dozens of complaints, but that's arguably more of a germany issue). So now there's a fresh round of negative reviews on google maps, and I distinctly remember the company having two stars on google maps. Which they diligently replied to trying to individually slander us (as if anyone reads replies). I check again just now because they forgot to return kaution and, magically, all of our reviews are gone (mine says violated terms of service aka mass reported by a bot net) with at least 50 other one star reviews and they suddenly have 4.9 stars on google maps. The one review from any of us that AREN'T taken down is more recent - 4 months so 3 months after the other ones - the one talking about them deducting about 350 euro from kaution (the security deposit). At the start of the tenancy they asked for pictures of the room to show the condition, and he presumably didn't do it in a way that shows the condition of the furniture so they decided to deduct their full value (and likely not replace the furniture given the state of ours)
I don't have any other information about the others' kautions but I have an entirely different problem with it. I haven't received a deduction, kaution, any correspondence, or any type of acknowledgement that they I or anything exists. Right when I moved out they sent an email asking for the iban to send kaution to, and they just ... didn't. It's now been 7 months and I am about to have to write a letter demanding kaution be returned. My guess is that they looked at the pictures of everything I took on the first day, and then looked at the fact that I quoted the exact law justifying the amount to withhold in winter after they tried to trick me into an implied agreement, and decided that it's more risky to try a deduction than to just forget to return kaution hoping I forget.
Which I did not---I noticed the negative reviews experienced a mass extinction on google so now I'm here. If they were going to pay for our reviews to be removed why couldn't it be us?