My experience with them:
They were mandated by the new owner of the building where I lived in Basel. Building sold in the spring. We had an existing WG with 2 others, no Hauptmieter, all names on the contract, three separate deposit accounts.
They didn't contact us, didn't ask us anything.
They were informed by us (by mail) as soon as they took over from the previous landlord that me and another tenant were moving out (me to the other side of the country, her back to her home country), and that we were terminating the existing contract, with the third flatmate staying on with new flatmates on a new contract.
They waited until just before we moved out to respond and send documents to fill with the currrent, outgoing and incoming tenant information (apparently they didn't even know who lived there and didn't care to find out for two months before that).
Unbeknownst to us at the time, they then put everything in their files and with service providers (electricity and other utilities) in my name only even though the contract was in all three names, and even though I was just about to move out. I'm assuming this is the usual institutional sexism – funny how when I live with female flatmates or now with my wife, everything is always only in my name by default even when I'm not the main client, but when I lived with a male flatmate, it was always both names...
They insisted on not sending or receiving any forms by e-mail, only by post, even for things that don't require signatures (they should enter the 21st century, but okay, fine), but then the agent in charge of our building went on holiday for two weeks and nobody else processes the mail for their portfolio while they're away.
That led to them not finalizing the termination of our contract and creation of the new one, so everything apparently stayed in my name after I moved out.
Except the billing department did open a new file with a new reference number, and stopped monitoring the cashflow to the old ref. number. But since our agent is away, nobody sends the new payment slips, so the new tenants and I have no idea, and my former flatmate who stayed on just had just kept paying the collective rent on the same account we had before.
In August, I receive a Mahnung and notice of collection action at my new address (because they still had everything in only my name and I set up mail-forwarding...) for unpaid rent. Since they stopped monitoring the old ref. number, they didn't see that the tenants had in fact been paying rent, just on the old (and to our knowledge at that point, only) ref. number. Pretty insane to receive a Mahnung for money I don't actually owe from a a company that is at that point sitting on my deposit money.
Eventually we receive the payment slips for the new contract.....at my new address, and in my name.
They insist on not using the forms provided by BKB for closing our deposit accounts, and using their own forms for that instead, which we receive...at my new address. I then have to mail that to my former flatmate, they have to collect everyone's signatures, and oh! my other flatmate moved back to her home country, and some of the new tenants are away for the summer, but now we need their physical signature too...
Their forms are wrong and we keep telling them, but they won't listen. They assume we have only one rental account and need to change the names associated with it. It took weeks for them to finally get in their heads that we had 3 separate accounts, and that we very simply had to close mine and the other and have the new tenants open new ones...
They then sent the forms to open the new accounts for the two new tenants, whom I don't know and haven't even met....to my new address. It's now over 2 months since I moved out. This could all have been solved on week 1.
They refuse to close the deposit accounts for me and my other former flatmate because they "can't release our deposits until they have the new tenant's deposits set up". Since it's not the same contract being handed over, but a termination of the contract with creation of a new contract (they said it themselves), this should not be the case. In the end they finally released the deposits after more than 5 months.
Now in October, I got an electricity bill from IWB, for the months July to October (I moved out at the end of June and the new contract was supposed to start 1st July). Agency assures me they will update the files with the service providers so that things are not in my name anymore.
At the end of last week, Mahnung from IWB for that electricity bill, in my name, at my now not-so-new address on the other side of the country. They never updated the files, the actual tenants never received the bill, and so never paid it.
They've been told repeatedly, by phone, e-mail and post, that I don't live there anymore, don't have my name on the contract anymore, and shouldn't have anything in my name. I just don't get it.