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It is recommended that your application not rely on the information retrieved from GetItem or GetSellerList until 30 minutes past the scheduled ending time of an auction. After an auction completes, a batch job is kicked off to finalize the relevant database records. In certain high load situations, this may result in a significant delay. In a vast majority of transactions, the time will actually be quite small, but to avoid missing a transaction, the 30 minute buffer period is recommended.