I hope your email to ebay was easier for them to understand than your messages here have been as it is about as clear as mud to me.

 From the title of this thread, it sounds as if the problem is you were overpaid-that the buyer included postage costs when they picked up the item.

I am surprised that you (or whoever you arranged to be at your home in your palce) was not aware of the amount of money to be collected but if you have been overpaid, then do as  davewill suggested and refund the postage component.

If, on the other hand, you feel you have been underpaid (which you seem to imply in your later post) because the postage component was not given to you, then you need to realise a lot of customers will choose to pick up an item, rather than have it posted, because they assume that pick up is free.

You didn't post it to them so they would not pay you postage cost. Only the item cost. 

But if you are talking about ebay fees, then if you advertised an item with postage plus pick up available, then I guess ebay might have deducted fees for the postage component? Is that what you mean? I think that if you arranged pick up, you would need to enter a special code. If ebay does not know this was a pick up, if you have not marked it as such, then ebay would charge fees on postage. 

Hope in one hand, do something else in the other.

eBay emails are answered, if at all, by bots.

You will need to provide some pertinent facts if you wish other members to help you.

From the very limited information you have given, if the buyer paid for postage then picked the item up, refund them for the postage component of the sale price.

No need to involve eBay.