I just returned from a 5 day trip to Marrakech w/a 3 day excursion to the Sahara Desert (on the other side of the country). I've traveled to over 30 countries around the world, this was not my first time in a 3rd world country. I've never in all my traveling met locals who were so rude, nasty and ungrateful. I'm sure since you're on this sight you're familiar with all the common "travel schemes": the child who walks you to your destination when you're lost then demands $, the man who walks you to his friend's shop, the guy who claims he's selling his goods to you at the same price for the locals. I've never seen it SO bad as it was in Morocco, they have perfected scamming. Walk through the square and someone will THROW a monkey onto your shoulder, let you snap a picture then DEMAND - I'm talking YELLING and screaming - money from you, and no matter HOW much you give, it is not enough. You WILL be chased through the square. We tried to pay the snake charmer BEFORE we took pictures to avoid such a scene, he says "it's good, it's good, pay after" When we tried to pay him $16 after we snapped a few photos he went BALLISTIC, you would have thought we murdered his first born daughter the way he was yelling and screaming. Seriously, we gave him $16 (to take a few pictures of his snake) which is probably enough for him to live off for 3 months and yet he still yelled and cursed and chased us. It really ruined the entire experience. Shop keepers are the same. We bought a bottle of water for $2.50, the next day we asked a local tour guide sales man how much a bottle of water SHOULD cost, .75cents. Another day we ran into a boy who offered to take us to the Jewish market - "which is only open once a week" - completely UNtrue, it's open EVERY day. He took us to his friends shop who claimed all prices are the same for locals & tourists. Of course the prices are weighed in grams, so when you think you're buying something for just a few $, he puts the item on the scale and your total sores. From that point on I couldn't even bring myself to look at anything in the shops or even try to interact with the locals. Many people on my tour felt the same way.
Which brings me to my next point. If you're thinking of traveling to the Sahara Desert from Marrakech, think again. You will spend the next 3 days in a van, most likely smooshed next to 7 other people. The first day you'll drive about 8 hours stopping briefly to see some sights and lunch. The next day about 4 hours of driving, again with stops - one of them being to a carpet sales person - the carpets looked pretty mass produced to me. Then, you'll finally arrive at the dunes around 5pm. Off into the desert for a 1 hr camel ride. Then it's up at 5AM for an 11 hour van ride back to Marrakech. As much as i love riding camels and climbing sand dunes, it was not worth it. And lets hope you don't get car sick as a good 2 - 3 hours of that drive is spend winding back and forth through Mt. roads.
As for Marrakech, you only need TWO days there MAX to see everything. We saw everything in a day and a half. And FYI, the tombs, yeah, they'll take you about 5 minutes to walk through. After going to Marrakech / Morocco, I'm really surprised at how many positive comments there are about the place. Of all the places and countries I've been to, this one was by far my least favorite. My advice, if there is somewhere else you are considering going to - go there instead.