This isnt a bug, it is a mistake, user error.
You will likely find that you were asked to post it as a bug report by the employee because thats where you report bugs, im not trying to be deliberately sarcastic here, there is just no other way of saying it without sounding that way… anyway this serves a few purposes, for example if other players come across the same issue as you have here, a search of the forum may help them with a solution to it if its something that can be performed by the player without the involvement of a customer service rep, then if a bug or issue is very common, they dont need to individually reply to every single player that has it when there are already posts easily accessible about it. It is also very likely that even if they know it is not a bug, they would still ask you to post here about it so that a developer can confirm this. Ask anyone who has worked in any kind of customer complaints role that when a customer wants a refund or compensation for something which is due to their own error, it is more likely they will argue about how this isnt acceptable, the customer is always right, even when they are wrong, and they cant be wrong, because they are always right, and because of the emotional distress they have caused, they now want compensation ontop of the refund. This is either due to the player just not understanding the system in use, or pride, why accept a personal mistakle so costly when there is a chance that youll get a refund claiming ignorance.
Just asking you to report a bug by making a post on the bug reports forum isnt him confirming you had a bug, its him doing his job.
When placing a sell order the listing fee is displayed above the cancel button in large bold text, your remaining balance is showed to the right with a separator between the two.
The confirmation you are saying should come up, is there already, its what you clicked on to place the sell order that you “lost” 10k in the first place. It is that entire window, you have rushed through it and listed something at the wrong price, unfortunately it has cost you 10k gold… I will admit I have done similar things myself before, not at that much of a dent to my total gold, usually happens when im tired and listing a load of crafted tools, a few times ive listed all the pickaxe’s ive just crafted as thats all i had on me, then realized afterwards i had steel ones in storage that i had massively overpriced and paid the listing fee on…
Also, your step 4 on the list to replicate isnt how the trade sell order window works. By default the price that comes up per item isnt 100, it has the price from the last thing you searched/listed, it only changes to 100 if it doesnt find anything currently listed on the search that was just performed. If it has searched and timed out due to latency etc, this will behave like there are none available, again this isnt a bug it is the search timing out due to how long it was taking, this would in my opinion be a “feature” do avoid people getting stuck waiting for it to update, and due to the fact it already shows you in the biggest numbering in the whole window how much the listing fee is, all I can personally believe has happened here is like what happened to myself youre attention has switched off a little and youve clicked confirm without adjusting it or searching again.
Personally what I believe has happened here is that you havent lost 10,000 gold to a bug, you have spent 10,000 gold in error on the listing fee in a rushed auction posting.