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"The price points in this graph were calculated by determining the average selling price on eBay over the last 14 days for this item in the condition described above [i.e., either New or Used], excluding outlier selling prices as determined by eBay in its sole discretion from time to time, and does not include shipping and handling costs. No representation is made that particular item will sell for a particular price."
I accidentally enabled that graph of previous prices to show up on Ebay, but I can't figure out how I did it.