Horribly wasting time.
On oblivion fof 360, you can set the amount of items to sell to one by tapping the left bumper.
My mercantile skill was piss poor, as I tend to hoard items in rpg's. I got my hands on the "Robe of glib tongues" which slaps a +8 on merc, then grabbed a pair of "boots of the swift merchant, which adds +10 merc points.
Since merc is set by number of transactions, rather than amounts, I loaded up on iron arrows, because they aren't worth poo.
According to a wiki, you need 25550 transactions to go from prison escapee to master merchant. Since I graduated from the walter white school of alchemy, I had a shitload of potions to go with the arrows. With the robe of sales and shoes of fypm, I managed to get mecantile to 78, which tripped thd ability to invest in stores. And even better, unstuck me from a snag on the mages guild questline.
I think this might be my last go-around for oblivion, the merc grinding really sucked out the fun.
