You are awrae that bots can undercut someone every few seconds, right? Just like a human player who watches the market board can undercut everytime someone undercuts them. This can prevent another player from selling their item.

You're right in saying that the buyer can choose who to by from, however, 99% of the time the buyer will buy the first item they see. And yes, other players can see profit potential in certain items, however, would they intentionally seek out and search for another player's retainer on another server? No they wouldn't.

If this was actual market competition, then why the need for the other player to hide their identity when they buy their items from other servers?

Why doesn't the other player approach my friend and explain that they aren't trying to stalk him?

Why does the other palyer need to change their retainers to match the names of my friend's retainers or name them in a way that calls my friend a scumbag?

Like I said the proof is on Goblin market board. And my friend is more than happy to show you the behavior of what this other player is doing.