Have we met someplace before? 我们以前在哪见过吗？

Sorry, you've got the wrong person. 抱歉，你认错人了。

I know you from somewhere, but I can put my finger on it. 我在哪见过你，但是想不起来了。

You have me mistaken for someone else. 你一定把我错当成别人了。

You remind me of someone I know. 你让我想起来我认识的一个人。

I feel as if we've met each other before. 我感觉我们以前好象见过。

I have the strangest feeling we've met before. 我有种奇怪的感觉好象和你似曾相识。

Forgive me if I'm wrong, but haven't we met before? 如果我弄错的话请谅解，我们以前见过吧。