Don't buy it. Do you're best to get out of there. If you are staying at a hotel get the first taxi you can and move it! If you are getting to the train station simply start walking out the door and down the road. It is less than half of one kilometer to the train station and only one road to walk on. Go through the gates and the train station is to your left.
The train station cafeteria is a safe haven away from these people. The local gendarme do a good job keeping the rifraf out of the train station. There you will not be hassled. There are NO lockers in the train station so if you are heavily packed sight seeing Tangiers may be next to impossible. Lightly packed you should be ok.
Now you ask, "But what happens if you get with a guide?" Let me tell you our experience. We were travelling with some other people we had run into so there were 9 people in our group. We ended up wasting a bunch of time that could've been spent on sightseeing inside shops with worthless trinkets. Now if shopping is your thing then this may be your cup of tea. But if you're into sightseeing you'll be highly dissapointed with a guide. Additionally, they try to persuade you into going to a restaurant. While we managed to not get suckered into that one, a couple we met did and ended up spending a fortune, which they did not expect, in the restaurant.