indeed it is Unfair for sellers to use these lines
a negative feedback will be exchanged by a negative feedback & we will try our level best to get compensation from you for this act.
The remaining text is actually a positive assurance to buyers that the seller is open for communication and resolve buyer grievances ...
Actually looking from a sellers angle ... his reputation and trading ability solely lies in his feedback and it is indeed natural for a seller to try and safeguard his reputation And at times we sellers do go overboard to avoid negatives :)... its natural
Just recently a seller on USA Ebay sued a buyer for leaving neutral feedback .
Though the case was dismissed ... the buyer did have to spend on lawyer fees to contest his case 🙂