Sell out as a phrasal verb has several meanings. It depends on the context in which you saw it. Sell out when it means to betray someone can take the object before or after the particle (preposition) unless it's a pronoun (me, him, us, etc). In this case it must go before. The Russian spy sold his motherland out. Sell out can also mean all items in a store have been sold, for example. This is a type of phrasal verb which has one particle or two depending on whether you specify in the object part of the sentence what is no longer being sold. For example: In its first week on sale in Russia, all the Iphone fives were sold out. or "I'm sorry sir, but we have sold out of Iphone fives." Make sure you learn phrasals in context when you study English because there are many nuances between our languages. For example, приставать might translate "to hit on someone" unwanted flirting, say, at a bar. However, in Russian, you also can say at work to your colleague who is bothering you with too many silly questions, "Что ты пристаешь, эй!???" "Why are you hitting on me" is not used to mean to bother someone in general. Your colleague might be shocked if you were having the conversation in English! ;) In summary, what this means is, sell out = быть раскуплены would be a potentially risky way to learn the language. Write down the example sentence from which you found the phrasal verb. Good luck.