Thanks, ebay have informed me that once posted I wont receive item as described (brand new and sealed) As hes already used the item. He informed me via ebay messenger that I could of made life easier by buying him 2 new 12 month game cards at a cost of £70. Clearly pulling a fast one..

If you get the cards back and they have been activated is there any way of deactivating them?

After you get it back you can report the buyer to ebay.   Buyers misusing returns is classed as abuse and you can report that here:
https://www.ebay.co.uk/help/policies/rules-policies-buyers/buying-practices-policy?id=4374

And be sure to put his ID on your blocked bidder list:
https://www.ebay.co.uk/bmgt/BuyerBlock

Good luck.

I've emailed Nintendo to try and establish when codes were activated. Once I receive everything back I'm going to put a claim in against the buyer to say item is no longer sealed and in a used condition as re-sale value will drop now. He's obviously trying to get £70 back off me. Sad thing is he accused me of being a bad seller and a lier. I know everything was sealed, I have the photo to prove it. He also had the cheek to leave positive feedback by saying everything is excellent 

Unfortunately, you can't "put in a claim against the buyer" because it is no longer sealed. Buyers are allowed to unseal their purchases. If they weren't, how could they return a genuinely faulty item?

You just need to work out if its value will have dropped more than £70, so would it be worth just going along with the buyer, even though you know he's "at it".

Personally, I would insist on the return, even if I did lose out financially. Regarding the codes, I would explore whether you could cancel them, but that may well not be possible. After all, although you bought them, you didn't activate them. To Nintendo, it would just be the same as you cancelling a gift, and they won't go along with that.

Sadly, whatever happens, it looks like you are going to lose out.

How much does it all weigh when packed ?.

Around 2kg 

It used to be that the default return label covered up to 2kg so i'm wondering if the item is over that would they still be able to return it and if not would they know that they would somehow need to contact Ebay CS to get another label issued to cover the weight ?.

Not 100% sure what iv'e said above still applies since SD came in as i haven't had to return anything for many years.

2kg fully covers the parcel however label i sent to buyer expires on the 8th. I believe this buyer has no intention returning the item, as he was clearly trying to get a further £70 off me. He became quite aggressive in his messages. He also said I could have made my life easier by giving him £70 for the online Nintendo subscription. I know everything was brand new and sealed and the main photo proves this. My issue is, do I continue to provide more return labels until the 22nd at my cost? He has absolutely no intention in returning this to me.

No return means no refund,you only have to provide 1 label.

You're getting silly now. Do you really think he meant that he would drop everything that instant and rush off to the post office?

You've done your bit, by issuing the label, and he will have been given a date by which he is required to return the item. If he doesn't return it, you won't need to refund, so don't sweat.

You've lost the £70 anyway, as the codes will now have been used, even if they hadn't been before, and your item will now be worth less that it had been before you sent it, so I can understand you being annoyed, but just calm down a bit.

Looking at the bidding history on it I can see the winning bidder has a feedback score of over 800. This is where eBay is a risk for everyone, bad buyers get more emboldened every time they pull this stunt and it works in their favour. 

You’re doing the right thing calling their bluff on the return. If more of us took this stand and the buyer knew they would have to follow the fraud through then they would think twice but sadly a lot of sellers cave in too easily. 

I must admit, I rarely give in to this kind of thing.

I would far rather force a return at my own cost, than let them keep an item.
It's amazing the number of people that just won't return, as all they were really after was an additional discount.

But it is one of those that you need to take on an individual level.  Some are very obvious that they are trying it on, but others, I will give the benefit of the doubt.