As others have said Its up to who the seller wants to sell it to. I think the "Dibs" post is pretty stupid and is always gonna lead to petty squables. I say if you want a item pm the seller, you dont need to post in his thread unless you have questions about the item. If the seller gets several pm's, they can simply choose the person who pm'd him first and post in the thread that the item is sold. Why make it more complicated than this?