Will you repeat it, please?
请再说一遍，好吗？

Would you mind saying it again?
请再说一遍。

I beg your pardon?
请再说一遍。

I´m sorry I didn´t catch your meaning. Will you say it again?
对不起，我没明白你的意思。您再说一遍吧。

I don´t understand what you say.
我不明白你说什么。

I´m sorry I don´t follow you.
对不起，我不懂你的话。

Will you speak a little more slowly?
请说慢一点。

Will you slow down a bit? I can´t follow you.
请再说慢一点吧。我没明白。

Will you explain what you mean?
请解释一下你的意思吧。

Could you be more specific?
能否再具体一些。