Apartment smelt bad, like stale cigarettes, rubbish from last guests had not been taken out. On…read morearrival the box containing the key failed to release the key and I had to wait half an hour and make three phone calls in order for someone to come and help. BUT WORST OF ALL Check Vienna messed up taking payment from the card I supplied on Booking.com, failed to ever tell me of this, then send an invoice as an attachment containing one line IN GERMAN asking me to pay. As no-one explained that the payment via Booking.com failed, I had no idea I was expected to pay. Fast forward two months later and a German debt collector is after me, and it's the first I've heard that payment didn't work.
BETTER YET the customer services at Check Vienna are the most rude and unprofessional I have EVER come across - including saying that I should have understood the German payment request MERELY BY IT'S LAYOUT and that they followed all regulations DESPITE BOOKING.COM SAYING THEY DID NOT FOLLOW THE CORRECT PROCEDURE UPON CARD FAILURE AND DID NOT NOTIFY ME OF THIS.
AVOID booking with them, not only was the apartment inconvenient and smelly, but you will need all the help in the world if anything goes wrong with your payment.