A thank you is really all that I think necessary - but I realise that others on eBay have their own preferences. Some truly love their feedback!
Like most people, approval gives me a pleasant feeling. It's not as pleasant as having some fine Belgian chocolate bestowed upon me, or a bottle of ruby port, but ... yes, approval, being approved of, seems to be something human beings find warming.
Hence the success of the green dot system.
However, meaningless approval (an automatic 
or โ
or ๐น or ๐) leaves a metallic taste of vacuity and the fibrous texture of hollow fustian in one's mouth - in my opinion. While I appreciate the giving of positive feedback from an eBay seller, and of course I leave feedback as a rule (as it's far more important to sellers than to buyers), I'd rather purchase from a good seller who has the items that I want to buy, than from a good seller who doesn't sell items that I want or from a poor seller whose behaviour would make me disinclined to enter into a transaction with him - irrespective of whether any of these sellers give feedback to their buyers.
In fact, if a poor seller gives bright glossy green feedback with one of those obsequious "Best buyer EVER" sorts of comment, it would be insult to injury, surely...?
โHe does me double wrong
That wounds me with the flatteries of his tongue.โ
