I'm thinking through citing an item for sale on ebay. It's a check with a signature on it that shows the person's signature on a specific date, before they changed it to another spelling. Do eBay listings get cached by the Wayback Machine? To be safe do I cite the whole listing URL in the footnote? Once it's sold the "repository" will be unknown. Is that a problem? Is it better for me to buy it and state ebay as the provenance and me as the repository? Too may questions?