If you want to get more money; identify your items because identified items are more valuable than unidentified. You also get more money if you repair items before selling them. For example if you repair any item for 100 and its value was before 200 now its value will be 300. An easy way to get extra money is in Tristam (act I,the Cairn Stone Quest). Find Wirt's body in the top left corner of map. He gives up quite a bit of money. If you save the game and exit to the title screen then start the game again you can keep going back to Tristam and getting Wirt's money.