I am very strongly against any idea making trade between players possible. What they'll all end up doing is make the game easier and more exploitable.
It offers many exploits. You could use it to transfer money between players, have multi-accounters hoard their money on a single account. It will eventually be possible to spot your own sales, especially when you sell unusual items no-one wants. Like broken bottles. Who will by those on the market when you can get them for a scrape in a store, even with 4x price?
The option for not making your own sales visible will ADD to the ease of finding them! Use another account, find the item that's missing from your own inventory and you're done!
If it becomes possible for products to be traded, why even bother making some items hard to find? Just by em from the auction house. The you really ensure that people only do the best jobs available. Maybe it will limit the jobs people do even further to only the most lucky jobs, because hoarding items might very well be the most profitable thing to do.
If this idea serves to push item prices ABOVE regular store prices, why bother? Everyone would go shopping in the town that has it in one of their stores.
I think this will eventually degrade the game's economy and item values below a playable level.
You can't just introduce this without SERIOUSLY considering the impact on a game's economy. If it was wanted, it would have been there. It's not like it is that difficult to implement this. It's just that the gameplay effects are severe and drastic, and it could end up ruining the game experience all together. Unless the devs are really serious about a leap of faith into the future (that could end up very bad), I very strongly oppose this addition to the game.
The only possible option for keeping the economy slightly viable would be to remove all stores. Only then will items be rare enough for them to retain actual value, and will this system be interesting.