When you start in Riverwood, make sure to not talk to the miscellaneous goods store owner and sister. Instead, go out and increase your Speech and take the perk to invest in other stores. At that time, make your first investment with the miscellaneous goods store owner. From now on, every time you make an investment in another store his available money increases. Added with the perk of all venders have an extra 1,000 gold available, he can have over 10,000 gold available, which makes him the richest vendor in the game. That also makes finding and selling things easier, instead of running around to all the vendors in all the different towns.