导购口语:

If you have the receipt, I can relace it for you.
如果您有发票，我可以我给您换。
You can exchange it, Provided that you haven't taken off the tag.
只要你没有把吊牌拿掉便可换货。
I'm sorry; I can't exchange your shirt without the receipt.
很抱歉。没有发牌，我不能给您换这件衬衫。

语句解析:

Replace替换，置换，代换；exchange交换，调换，兑换。换货时，需向客户说明如果您有发票，我可以给您换。你就可以用这种表达：If you have the receipt, I can replace it for you.

情景再现:

I wondered if I could return it.
我想知道能不能退掉它。
Goods can be exchanged only on production of the sale slip.
只要出示销售单（小票）就可以换货。
Please produce your receipt if you want to exchange item/
如果你想换货，请拿出收据。