I want to give the seller bad feedback. I was prepared to pay $290 over his asking price; now I have no proof because my snipe was not archived. I joined SPECIFICALLY to buy this item: if I have no proof that my bid even existed, what good is my membership?

Hello Michael,
Thank you for your question about this item. The seller did nothing wrong here. A buyer offered $460. You could have done the same thing.
There is a record of the snipe on your Completed page, but technically, the bid never existed because the item already ended.
If the item comes up again, check to see if it has "Best Offer" enabled, and you can approach the seller to try to get a low price.
Thank you for taking the time to write in. Please let us know if we can provide any other assistance.