The product has been sold out.为何不用被动,没有been呢?奇怪

这是特殊用法，表示东西被卖完了用主动表被动
比如说this kind of product sold well(这种产品买的很好)
上面那句是被动，但是我觉得是你多打了个been

这个已经是被动的了呀！

应该是 the product has sold out.或者the product has been sold out.都可以.
有些词是“主动表示被动的”
像：Her new book sells very well .她的书很畅销.
The coat feels soft.这衣服穿起来软绵绵的
Ice-cream goes well in summer.夏天 冰淇淋卖的很好.
以下是《朗文当代英语辞典》中二者区别：
be / have sell out:
1.if a shop sells out of sth,it has no more of that particular things left to sell （如果一家商店的货物脱销了 没有专门留下的来卖 就用 be sold out.强调“本家店”没有了,其他店或许还会有.用be sold out）
e.g.Sorry,we're sold out.
2.if a product,tickets,places at a concert sell out,they are all sold and there are none left （如果一个产品,音乐会的票,卖光了,全部卖光,“片甲不留”.强调已经没有机会得到此物了,用sth have sold out）
e.g.Wow!Those scarves sold out fast!
be sold out
e.g.Tonight's performance is completely sold out

该产品已被卖完。不奇怪，是被动句，有been。