Even though there are essentially no tourists going to Liberia there are four concentrations of craft shops in Monrovia. They apparently live on the trade from embassy, aid group and UN employees. The largest was on Mamba Point near the US embassy, but it has shrunk during the last year due to construction and government clearance of illegal occupancy, another is four or five blocks away in front of a hotel where some permanent structures were built for crafts shops, and the third and fourth are to be found on a couple of the streets downtown. There are all actually within walking distance. You will also find a scattering of stands usually with carvings but also some with baskets, along the main roads in and out of Monrovia.
Traditionally the Charlies were traders most often of the Mandingo tribe. The people involved are more varied at this time. Still most of the people you will see are tradesmen not craftsmen (or women). Bargaining is always required for a fair price.
What to buy: Made in Liberia is harder to find than you would expect. Much of what you see is from other African countries. Carvings, paintings, cloth are frequently from the mass producing shops in the Ivory Coast, the Congo and Ghana. Even much of the bead jewelry and many of the masks come from outside Liberia. The craft traditions of Liberia are recovering but the quality of the past has yet to be reached. I did find a group making leather sandals, something I had not seen in the past. If you have time, you can have tailor made shirts and outfits from African cloth. The tailors use the old mechanical (non-electric) sewing machines. The challenge is finding the tailor who will sew it correctly the first time and have it ready on time. (Liberian craftsman never have had a great business ethos.) Expect to make multiple trips to the shop to pickup you items. Expect to have to bargain for a fair price. During this process you can expect to have a demand made for some cash up front. I would recommend that you resist this demand, especially if you bring your own cloth or are on only a short visit.
What to pay: A lot less than the asking price.