if you get them at low level, no, later on they become pretty good, and thieves guild fences dont have more gold than normal traders :\ so if thats your only reasoning its not worth it over the weapons and armor that you can get from there if you wait

you can just join them btw so you get a place to sell stolen stuff but dont finish the quest line, also if you do 5 side jobs in every big city(the ones that have walls xD) you can get 1 trader for every city to come to the thieves guild headquarters. after uve done 5 side jobs for each city ull get a special task. after you join the guild they will tell you from who you can get these jobs
