Hire trailer allegedly returned damaged

Hello together, my question doesn’t really have anything to do with “insurance”, but I think that this forum is best suited: On Monday, July 10th, 2011, I borrowed a trailer to bring wood leftovers, an old sofa, etc. to the tip, along with three other people. So hangers half filled, off to tip, emptied, swept, and brought back to the rental location. None of us four even noticed the smallest Macke on the trailer. On Thursday evening, that is several days later, a call that the trailer on the Deichsel – ladder wall is badly damaged, I am the last tenant and should please look at it. I went there on Friday together with one of my helpers, and see there: The damage was already seen from the road: The cover rail at the front was in two places through broken, and the left ladder wall torn out of the screws, which could also be clearly seen from the inside, because “the sun ran through”. No one had seen this all days, not even the person who had put the bullet fuse back on. And neither did we, when uncoupled, nor when sweeping, nor when bringing back. Now I am supposed to pay the repair, but I am absolutely not aware of any guilt, which my three witnesses also confirm: The trailer was ok at the delivery. ? Rising heavy guns? Refuse to pay? I’m a bit perplexed. Thanks for reading and also for any tips. Gruss cube