I’d like to return this.
我想退掉它。

Can I have a refund?
能退给我钱吗？

Could you alter this, please?
能改变这个吗？

The waist needs taking in (letting out) by 3 centimeters.
腰需要收（放）3公分。

Could you make it longer (shorter)?
能做长（短）点吗？

Does it take a long time?
要用很长时间吗？

Can you make it a little earlier?
能早点做吗？

I put money in this vending machine, but a coke didn’t come out.
我把钱放进自动售货机里，可是没有可乐出来。