The only reason you should be posting on a trading post thread is to engage in the buying, selling or negotiating of the trade of goods being offered or sought by the thread starter. Disagreeing with a user's practices/ethics/morality in how they conduct trades is not an excuse to ignore the forum rules and post harassing messages targeting said user. If you want to give the item away for free, you should create your own thread to do so instead of soliciting it here.
Moreover, reporting the thread because you don't agree with how the thread starter is doing their business is not an appropriate use of the forum report function either. It's not a dislike or disagree button, and misusing it is considered a form of abusive behavior.
Lastly, because no rules are being violated by the thread starter, this thread is being allowed to remain open. If an item can be exchanged through the in-game trading system, then users are free to set their prices however they wish, so long as the price is for in-game trade-able goods.