Response from Carmen:
concerning the bath issue: I had checked the drainage before arrival as usual and it was all ok (the bath and all tubes are almost new!). Drainage blocked later probably due to some hairs. But I'm always reachable (by email or mobile) and I would immediately fix it. But guest didn't give me a call or didn't write me a message (there is a small Internet-Shop around the corner with phone and wifi). So I couldn't help.
concerning Check in issue: I sent the email with the details twice - the guest didn't receive them?! Until now no guest before had a problem with check in. And if really somebody has an unexpected problem we will always help as also happened in this case. Here it was an expensive international call to the guest.
concerning Wifi: I told the guest several times before booking that we don't (and won't) have wifi in our flat due to some security issues, but there is UMTS everywhere and an internet shop round the corner. So we recommended the guest to book another flat with wifi if it's really needed directly in the flat (airbnd offers many flats in Munich with Wifi, maybe not as stylish and nice as our ;-), but with Wifi).
But Guest declined our proposal and booked our (email hidden) guest know before that there is no Wifi. So it's no reason to complain afterwords.