Sell dragon bones/scales at the alchemist shop next door to Belethor. Sell gems, ore, weapons and apparel at the blacksmith at beginning of town. Bits and Pieces in Solitude is a general store and Enrith in Whitehold college is a general store. Sell magical items to a court mage ex: dragonsreach
All major shops only carry 750 gold besides the whiterun blacksmith. Invest in speech skills for the ability to make them have more gold.