I'm just browsing.

我只是随便看看。

Do you have this in a bigger / smaller size?

有大一码、小一码的吗?

Can I try this on, please?

可以试穿吗?

Where are the changing rooms?

试衣间在哪里?

Is this refundable?

可以退还吗?

Does this come with a guarantee?

有保修书吗?

Would you recommend this [name of item]?

可以推荐一款(某东西)吗?

Do you have anything cheaper than this?

有没有便宜一点的?

Can you give me a little deal on this ?

这能卖得便宜一点吗?

Can I have this gift-wrapped, please?

可以帮我包成礼物吗?

不要为没买东西而感到有压力。你可以这么说：

Thanks for your help. I might come back later.

谢谢你的帮忙。我还想再看看。