Marrakech is the destination on this site where the quality of your guide matters most. A good one turns the medina from an ordeal into the best part of your trip. A bad one spends three hours moving you between carpet showrooms and argan cooperatives that pay them a cut.
The whole game is commissions. Guides in Morocco have historically earned more from shop kickbacks than from their fee, which is why so many "tours" are shopping trips with a small amount of history attached. The fix is straightforward: only book listings that explicitly state no shopping stops, and read the most recent reviews looking for the word "carpet".
Book on day one
A three-hour medina walk on your first morning. It is the highest-leverage booking in the city — you learn the layout, you learn the prices, and the constant approaches drop off once you look like you know where you are going.
Know what Agafay is
The single most common complaint about Marrakech activities is people booking an "Agafay desert" trip expecting Sahara dunes. Agafay is rocky desert forty minutes from the city. It is beautiful at sunset and worth the evening. The sand dunes you have seen in photographs are at Merzouga, ten hours away, and require two nights minimum.