OP is not suggesting that, generally, comments upset them.
But the Classified sub-forum is there for a purpose: to find buyers for items. And it has specific rules to which the vast majority of Chatters adhere.
People commenting that x item is poor value for money or that the item looks in poor condition adds no value and is to the detriment of the sub-forum's purpose and may deter people from offering stuff for sale - see
@kingrollo's recent Brooks saddle exasperation.
You may think your comment is fair, but you aren't the seller nor have you seen the item, nor it seems are you a potential buyer.
My grandfather's recommendation was to ask yourself: 'Is it true? Is it kind? Is it reasonable?' Any one 'no' - think it by all means, but probably better not saying.