Did you make sure you are the last to reply in conversation? Speed of reply don't matter as much (As long as its within 12 hours), just make sure you are the last person sending out for it to count. This is why when seller chat with other seller it becomes problematic, I always find myself spamming stickers with other sellers until they either give up or block me. If they block me they lose because most people don't know the one that blocks are counted as if they didn't reply.

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I think you should make it Mall>preferred>total sales+rating because its a common thing for preferred badge to be removed for a certain time with simple penalty points, you will see a lot of big sellers temporary losing preferred status during peak sales day due to late shipment