Is there room in the title to add "size 3-9"  -  might as well make it crystal clear.

Unfortunately no, cause I don't want to delete any key words in the title.

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@liquidationhouseffi wrote:

Thanks everyone. Will try and see what will happen. But I guess the socks may have been worn.

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I wouldn't mention returns in your first reply, if it's not too late.  If she does want to return them, state that under the health regulations you can't accept anything back if it's been worn and not in the original packaging.  If she saw the size on the packet and decided to try them on anyway she made it her problem if they didn't fit, or that's how I see it.