Good evening, I would be happy to assist you with this question.
Given that you clearly sold the item "as is" and they had an opportunity to see it when they bought it, you have no obligation to refund their money or give them any rebate on the price.
As with all transactions, even moreso for private transactions on used goods, the caveat "buyer beware" holds true and is upheld by the courts. A person buying a used item has an obligation to know what they are buying and the terms upon which they are buying it. They also had every opportunity to inspect it prior to completing the transaction.
The only way that you would have any exposure would be if you intentionally misrepresented something. From what you've described, you made it clear that the trailer was sold "as is" and again, the buyer was able to see it before completing the transaction.
I hope that this information has been of assistance to you. I am happy to chat with you further should you need anything else either now, or in the future.
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