I'd sell a sparse amount from each item category, but I'd have a large amount of money to buy with and a very high mercantile skill. In other words, I'd be the only person you can go to to sell anything over 2000 gold, but at my prices you'll only get 1000 for it (because face it, selling it at 50% with a max potential of 1200 gold is better than selling it at 70% but with a max potential of 600 gold). Then, with my superior mercantile skill and my knack for attracting only high-end adventurers, I can make shit-tonnes of money as I sell to every other adventurer, because face it, if everyone sells to me, then only I have the good stuff, so then everyone has to buy from me too.
So basically I sell almost nothing of my own, I just buy and sell adventurers' stuff for massive quantities of money, meaning I'm everyone's best merchant friend.
EDIT: And in case I was far les sobvious than I thought, I have been playing oblivion lately ... but you know what I've noticed, apparently there has been a boom in teh oblivion play-time, why is that anyway?