And don't play it too safe with the items you buy to sell; the more expensive items are often worth the risk (to an extent, of course), as you end up with considerably more raw profit, even if you're moving less merchandise; you can't just sell cheap stuff. I didn't know about the whole 104% thing until I'd already beaten the game, and I managed to get through it on a single play-through by selling the right items; barely, admittedly, but I did manage. The Jade Way is worth getting through, by the way; the item you get at the end of it should more than cover your first week.
Oh, and of course, try to make sure you don't have any price-crash items on your shelves.
