Having empathy for the seller is one thing, but I can't go so far as to say their actions are acceptable just because the reasons behind their decisions may be understandable (that phrase is probably gettin' a bit old, but I think it's an important distinction to make). For a more obvious example, it's understandable that a seller wants to get the best price they possibly can when auctioning an item, however it is not acceptable to engage in dubious practices to acheive that (shill bidding, misrepresenting item condition, etc).
I'm all for cutting sellers some slack where warranted, probably have a stronger bias towards sellers in a lot of cases, and I'm not suggesting the buyer should be enraged and do as much damage as they can, or anything even remotely like that, but I'd be a little annoyed by something like this.
JMHO It's not that the seller wouldn't combine postage post-sale - this isn't quite like when a buyer purchases several items, asks a seller afterwards if they'll combine postage for a reduced cost, and the seller just says no and sends a combined invoice with the postage tallied at the full amount while actual postage is a lot less than paid, and the buyer getting a bit hot under the collar because it feels unfair.
It's the false excuse, whether originally intended or not. At the simplest level, it's saying one thing and doing another. In my mind it's not too far removed from advertising free postage, then invoicing with postage costs added (in the sense that it's saying one thing, doing another, at the buyer's expense). I might ultimately dismiss it, sellers have mildy aggravated me numerous times over the years, with similar practices where a simple, polite but curt message was sent (by me), and that was the end of it.
If they had been up front and honest, or acknowledged postage could be combined afterall, this thread probably wouldn't exist - instead they said it wasn't possible, because it was too late, but it clearly was possible - that's what would bother me. Whether the seller discovered that before or after the second label generation is irrelevant, because they were aware the buyer had queried combined postage, and it would seem they made their decision knowing what they'd told the buyer, and what they ended up doing, were contradictory, and I can't see how they could have made that decision without expecting the buyer to go 'what the...?' upon receipt. 
Whether or not the total price was ultimately a good deal is irrelevant to that - cheap items, or good deals, don't excuse sellers from less than stellar behaviour, just like spending wads of cash doesn't excuse buyers from less than stellar behaviour.
Well. I'm going to be the odd one out, here.... (not unusual for me though LOL)
I'm sick of all these 'what if's' and 'you still got a bargain at that price' comments.... FACT of the matter is buyer bought two items at a winning price. Seller told buyer items had to be sent separately, please pay two postages.
Buyer was happy to do that and did. ALL FACT!!!
HOWEVER....... also FACT.... Seller has sent items as one parcle, costing one postage!
Seller is in the wrong. FACT!
Seller is NOT ENTITLED to keep the two postage payments when he only used one!!!
I'm on the buyers side here. I'd be peeved off too. Especially since seller claimed first winning item was already packed and courier organised.
The OP could (not should, but could) email the seller and politely ask for a partial refund on postage since seller sent both items in one parcle. I dont know if the OP could report the seller for making a profit on postage costs or not....
Depending on the sellers response, if he gives a refund, green dot.
If he says rock-off, then definately give a red dot with 1 star ratings all round.
Cheers folks... 
xxj
Hdepending on the volume of sales a seller makes, some will pack each and every item they sell once they have taken photos and listed the item. Some posters here on the boards have said that they do that with items they have listed ( not on this thread but on other threads).
For this reason, it is not unreasonable to take a seller at face value when they say shortly after an item has ended and been immediately paid for that it is already packed. It may only need a label to be attached.
The OP waited half an hour before messaging the seller and asking about combining. Once they saw the other item they could have messaged and said "I am interested in another of your items and will be bidding on <item title> and would like you to combine the items should I win this other one if possible" . Instead, they waited until after they had won the second item, in itself not wrong, but it may have put the seller on the spot and they responded inappropriately. Given time, they may have responded differently in the hope that the buyer would bid more aggressively to win the second item.
edited to add: wagon wheels rock, just ask padi and tippy! Here's one from a batch I made last week The hole in the middle is from the skewer I used to hold it while being coated in chocolate - 70% cocoa chocolate that is
