Feel free to bargain and if the price is still unfair and the vendor won't budge, just walk away. Once you make some African friends you can enlist their help in purchasing things if you wish. When buying souvenirs, always bargain. The vendors will expect you to, and not bargaining gives them the impression that foreigners have money to burn. The most common crime is petty theft.
Taxis are inexpensive.
Don't carry valuables in a bag or purse. Keep them on your person. When carrying important documents or large amounts of money, use a money belt. Always be discreet about your money. Don't flash large bills on the street.