Yes. I sell on Ebay and state in my auctions I will cancel bids from buyers with more than two negatives, and I check all my buyers feedback they leave for others.
Some people unfortuantely leave negative feedback for sellers like it's going out of style and if I see a potential buyer has left a lot of negatives, I will contact them and ask them about the situation.
I have canceled bids from people who refused to tell me.
*Was the item misrepresented in the auction?
*Did your childs teacher tell you why the item was no good?
*Just because the teacher says it could not have retailed for $600 does not mean it didn't. The seller may have been ripped off when THEY bought it and not even known it.
*Does the seller have any other negatives?
*Have you made any contact with this seller since you bought the item?
My personal opinion, I'm sorry to say, is if I were the mediator in this situation, I'd have to take the sellers side. You purchased this item months ago and are just leaving negative feedback now. This person probably assumed you were happy with the sale and just forgot to leave feedback. Unless of course the listing claimed the item was brand new and in perfect shape, but even then, I'd question why it was not brought up when you recieved it.
Just my opinion.
Did you use Paypal? Paypal will 99% of the time side with the buyer, even if the seller has done no wrong regardless of the circumstances. If you feel that strongly that you were wronged, you can always use Paypal to charge them back, although I think it's a very mean thing to do.