Weeell... I would say that it should be easy to keep track of which items to sell and buy, but I know that things are never simple. What with these new items often having names longer then you can read, it\'s easy to mistake them. Before you had to click an extra time to buy and sell, I would have agreed that something should be done, but that bug is fixed.
As for marking things saved, there are already plans for containers. You don\'t see what\'s in the continers while shopping, so it\'s easy to just slap something in them and not need to worry about selling them.
Of course, containers are not quite ready for people to use yet. There are a number of bugs with them, the least of which being that you can sell a container and it will forget about what\'s inside

Kinda defeats the whole advantage.
Oh, and the idea of changing around the merchant window has been passed around.