But that's part of the fun, isn't it? As a trader you have to work on your reputation and keep track of others.
It doesn't work 100% like that when players have alts both in game and in this forum. Of course, you could say that you can have an idea about who's safe and who isn't, but that requires you to "know the forum", identify its posters, etc... In other words, there actually IS a Player-to-Player trading system, it's "The Market" section in this forum. Serious traders don't trade with random characters they meet in game. Serious trade is made via forum. This means that this aspect of the game doesn't exist in the game itselft but outside of it, in the forum.
Some people don't like using the forum but sadly it's needed if you want to become an "advanced" player: forum gives you access to better deals with other player, faction info, etc.
An important part of the game takes place in the forum and ideally it shouldn't be like that. Ideally you could experience 100% of the game without using alt+tab.
For example,TLA Mk2 (note to all readers: I don't want to start a silly discussion about which server is da betterest) offers a ingame market system (and also a player factions' database, but that's another feature). It works fine, even though it does have a few weak points, like lack of real interaction, as you only input items and values and it's all about clicking.
But anyway, the basic point to be adressed here is that it's kinda a mistake to say this game has no market system: there is already such a system which is not cool because it works outside the game.