This kind of skirts sells very well.为什么不是This kind os skirts are sold very well.使用被动语态

sell 可作不及物动词表示被出售:
To be sold or be on sale:Grapes are selling high this season.
也可表示吸引买主,销路好:
To attract prospective buyers; be popular on the market:an item that sells well.
这时候用主动语态.
This kind of shoes sell well.
这种鞋好卖.
这种鞋销路好.
这种鞋卖得俏.
Sell out 表示卖完了,卖光了,一售而空
可以视为及物动词短语,可用被动语态.
This kind of shoes are sold out.
这种鞋全卖光了.
也可以说:
The seller sold out this kind of shoes.