In Dakar, you have to work your way through packed streets of vendors. Biggest threat, being robbed. But..they can also put something in your bag. They will approach you and do not like to take no for an answer. It can get to the point of harrassment.
Unique Suggestions: Try not to go alone. Best to try and go with someone who can help escort you. In bargaining to buy..try to use a trustable local to barter for you if you can find one.
At the market, you are suppose to barter on the price. I wouldn't have known this if I wouldn't have been with an experienced traveler. Remember the conversions and about how much you would pay for the item if you were buying it at home, don't be uncool and pay less than it's worth.