I confuse the Buy and Sell panes...

[Venae Rell]

It may be that I am the only one, but I often get the Buy and Sell panes mixed when I am visiting a merchant, and have found myself selling my equipment by mistake. Argh!!

If there was a color change in the background for one of them, or something similar, it would help make it more clear which one you were using at the moment.  Or, if the background is hard to change, having a prompt asking "Are you sure you want to sell ______ to this merchant for _____ Trias?" would be equally helpful

[Karyuu]

I think a prompt may get annoying if you have a ton of items you need to get rid of - but a nice feature has been suggested a few times before: a way to mark items "unsellable" so that such mistakes don't happen. Thus they will still be in your inventory and you can equip them as normal, but they won't show up in the /sell window. I'm rather fond of that idea myself :}

[minetus]

or a drag and drop action would work also:
to sell - drag from inventory to merchant window
to buy - the oposite

[Venae Rell]

Aye, any of these sound helpful! Hopefully I will be more careful in the future as well.