...this is the exact reason we have a return policy requirement. Condition is subjective, one man's 99 is another man's 60, we can never legislate that fact. When there is a disagreement and the return policy is honored that is the very best we can do.
The essence of this post is anger at the loss of 500 euros, had the seller offered to make Michael whole this post would never have been made, all would be well. For you to call the seller dodgy is "inappropriate" as you have absolutely nothing to do with this transaction and cannot know the motivation of the seller OR the buyer.