There is no question that there could be possible abuse if anyone can contact a buyer, but that's the tradeoff. In some cases it could save the buyer lots of money. Because I was able to contact the buyer of a large collection lot from one of these UK sellers a few years ago, it ended up enabling the buyer to get an $8,000.+ refund through his credit card company. If I would not have been able to do so, he would have been stuck. In fact, he publically thanked me on the old Virtual Stamp Club. I ended up actually meeting him at the APS Summer Seminar a year later, so it was a gratifying experience for both of us. The point is that by not allowing anyone to contact a buyer,
ebay has enacted a rule which can result in serious financial harm to buyers. Since
ebay also has a rule against Malicious activity on their site, such people who might contact buyers could be weeded out if reported. So as I say, it's a trade off.
In fact, I am aware of three separate transactions involving these same UK sellers which saved those buyers over $20,000. total. And one of them was our own Sinclair, who I think got back $6,000.+ on his transaction. So the ability to contact a buyer can be huge.