导购口语:

We may either pay you an allowance or have the goods replaced.
我们或者给你折价，或者给你换货。
We could exchange them for you if you like.
我们可以给您换一双。
If you have the receipt, I can replace it for you.
如果您有发票，我可以给您换。

语句解析:

Pay you an allowance给你折价；have the goods replaced给你换货；exchange sth. for sb. / replace sth. for sb.都表示“为某人换某物”。

情景再现:

There is something wrong with the plug. I'll get you another one.
这个插头有问题，我给您换一个。
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。