Maradi is an easy city to get around in. The city center is very walkable, assuming you wish to brave the heat and the winding morass of unnamed streets. Few streets are named, and even when they are nobody knows them and certainly not the house numbers on them. When you're taking a taxi or asking for directions, the convention is that you name a landmark near the place you're going to. Each driver's inventory of landmarks is a little different, and he may call the place you're headed something different or in a different language than what you or your guidebook think it's called. Most of them know the names of the cultural sites, the major government offices, the hotels, the markets and major stores, the bus stations, the popular bars and restaurants, and so on. If you are making advance arrangements to meet somebody, you might think to ask your party what they tell the taxi to get there. If you know where you're going and are communicating well, you can also give turn-by-turn directions as you can once you've gotten to your closest landmark; be aware that this is a great loophole for a surprise fare increase possibly an honest one as the driver didn't know where he was headed in advance.
By Motorcycle-Taxis
If you need a little more excitement in your life or are that desperate to save 10 cents, you can take a motorcycle-taxi called a kabu-kabu. This can be fun, but it can just as easily be hair-rising. Many kabu-kabus in Maradi are 50cc Chinese motor scooters with only one seat on which you desperately cling in intimate contact with the driver as you whip through traffic. Professional kabu drivers have actual motorcycles with actual passenger space, but unlike in places like Zinder, the licenses in Maradi are not carefully supervised, and so you get lots of amateurs; worse, professionals aren't uniformed like they are in Zinder and so you can't always tell the difference. On the up-side, you are the only passenger, and so you go straight to your destination every time. Better yet, you can find a cluster of bored kabu-kabu drivers on every street corner, and you are almost sure to find one even at odd hours of the night when the taxis are all gone. A kabu-kabu ride starts at 150 francs; if you go any distance, that cost will increase more quickly and incrementally than a taxi, so the two are pretty much the same over intermediate distances and if you're going a long way the taxi is cheaper. The driver probably doesn't have a helmet, and certainly won't have one for you.
By taxi
Taxis cruise the streets with some frequency during the day; they can become scarce after sunset, even during prime nightlife hours. There is no taxi company, and it's totally acceptable to ask a taxi driver for his cell phone number so that you can call for a pickup, or to pre-arrange a pickup time, if you're in a remote location or out late. The driver might ask for a small fee to do this, but many don't, especially if there's a group of you.
Like everywhere in Niger, taxis in Maradi are shared; legally, the driver may carry as many as four passengers who may have as many as different destinations. It's possible that you'll pick up as many as five or six, especially if some of them are children, but if it is really starting to cause a problem for you and you don't mind being thought of as the 'entitled white person,' you can speak up. To hail a taxi, stand on the side of the road and hold out your arm; most Nigeriens will hold it out level with the ground, let their hand hang off their wrist, and make a beckoning motion. An American style cab hail normally works as well. The driver will slow down; tell him where you are going and don't get in until he says it's OK. He may have other passengers, and your destination may not be in the direction you're going; this happens and it's nothing personal. Taxi rides in Niger are computed in terms of 'courses' - i.e. one course, two courses, etc. Each course costs 200 francs about 40-50 cents. In Maradi, you will have to go from one end of the city to the other, or leave it entirely, to clear 'one course'. As in most cities, if the driver is going to charge you more, the etiquette is that he tells you when he's picking you up. If he springs it on you when the ride is over, you are within your rights to protest. His fare should also, legally, be a function of 200; that said, you'll often here a 300-franc fee quoted as a compromise with you; it's completely OK to agree to it.
In this author's experience, taxi drivers are more friendly, more honest, and less likely to try to take advantage of you in Maradi than in Niamey. Unlike in Niamey, you may reasonably assume that most drivers are giving you a fair price unless you know better.