Scratches that were already there
You move into a new flat. The floor has a few marks, you think nothing of it, you take no photos. Three years later, on your way out, the landlord points at those exact spots and demands 600 EUR to sand them down. Without photos from move-in day, it's your word against his.
Meter readings nobody verified
The handover is quick. Keys swapped, paper signed, done. Six months later the utility statement arrives: a 400 EUR bill for back-charges. The previous tenant's meter reading is written on it, but you have no way left to check whether it was ever right.
The letter after five months
You moved out ages ago and haven't heard a thing. Just before the six-month deadline runs out, a recorded letter arrives with a list of alleged damages. With no move-out report in hand, you've got nothing to push back with.
Same pattern in all three: without documentation, you lose. With photos, meter readings and signatures on move-in and move-out day, the money stays where it belongs - with you.