导购口语:

You can get a full refund if you have the receipt.
如果你出示发票就可以拿到全额退款。
We con't allow returns on sale items.
特价商品是不能退货的。
If ti had any quality question, you can have your money back.
若有质量问题，您可以退款。

语句解析:

Get a full refund拿到全额退款；refund作名词，意为“退款，退还，赔偿”；refund还可以作动词，表示“退还，赔偿”。

情景再现:

I'm very sorry. No refunding after it is opened.
很抱歉，打开后就不能退款了。
I'm afraid we can't refound you after it's washed.
恐怕洗过后我们就不能给您退款了。
We do not accept merchandise for return unless items are defective.
若非商品瑕疵我们不就收退货。