Why is this bad advice?
If you send an item abroad with a tracking number, it is only tracked as far as the hand-over to the foreign mail service.
You will not get confirmation that it was actually received - not even if you use Airsure.
Therefore, eBay will always resolve any claim that arises against you, the seller, in favour of the buyer.
Worse still, if you have a tracking number and decide on the strength of this to contest a claim against you, you will end up with a black mark because of this, and will lose your ‘Top-rated’ status if this happens more than once.
The only way a tracking number can benefit the seller is if the buyer makes a fraudulent claim within the UK, where the Royal Mail website will show that the item was actually signed for.