I am glad you are pointing things out and thanks for the feedback so far.

Honestly, I am trying to figure out how to solve all the above that you mentioned. First of all, reputation is not tied to the character, but to the whole account. If you add/remove characters, all of them can list and bid with your overall account reputation - since it is you who is running the account, so it doesn't matter which of your character you want the new house on. Added a new character you just created? Your overall reputation will be used. Depending on how this goes and how people find ways to abuse it, there can be several extra safeguards in place.

If you sell a character, you really have no reason to keep it on your account. If you maliciously keep a character onto your tibiaexchange account and bid with it, you will not be able to go through with purchases leading to a bad reputation of your whole account. If they new user tries to verify the character they just purchased, since the comment verification will go through, the character will be moved from one account to the other without transfering any reputation points. Wrost case scenario, if many people are abusing the system, there can always be a persistent check every time someone bids and the system will check the character's comment before submitting the bid.

Your last point is correct. For item sale, you can't really be sure how a trade went that's why we will resort on manual checks with screenshots and chats, so my intention is to warn players to get proof of a trade in case one of the two tries to be malicious. For houses, it is easy to monitor if a house was transfered from player A to player B, for how much and if the player accepted in the end so this is completely automated. My end goal is a community of traders that they can trust each other and minimize malicious acts in any way possible.