Problem with combined postage

[mygirllollipop]

This is the second time I've encountered this problem. Someone won two items I listed and when they've come to pay they have only paid the lower postage. I have said wait for a new invoice with combined postage if they win more than one item yet they didn't.
Is tehre an option I can tick somewhere that I am missing?

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Thanks KOMH - do you think she'd accept that or will she get angry?
If anyone knows the wagic wand answer to stop this happening again as I am about to list loads, TIA.

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They cant do that! You are in the right here.
If they want to rush and pay before you have got the invoice sorted then they should be paying both postage charges.

I don't mind combining postage and together the two items come to what the heaver item came to, so I would have just put the heaver postage don't for her.
KOMH they were nearly the exact words I used on teh listing! I had put that I combine P&P and to WAIT for combined invoice. This didn't stop her, I want something to physically stop her! Because I am too daft to cause a fuss and really don't know how and why paypal let's them do this. I have posted them now - grr.

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Postage rules are 'add amount for each additional item' or 'subtract amount for each additional item' which I am reluctant to do due to varying weight of items!

I can stop buyers combining payments, which means paying both postage amounts. Then I can send my own invoice? Buyers won't know until they come to pya - would they think it dodgy?

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