We spent an entire morning in the souks at the beginning of our trip to Marrakesh. We hired a guide to take us around which cost 100 DHM (about £8) - this was definitely worth it. The souks are a complete maze and there is so much more to see than you would expect, so hiring a guide so you can see everything is advisable.
Make sure you haggle! We ended up spending a small fortune in a chemist shop in the souks buying Argan oil and spices. We did ask our guide once we left the shop if we should have bargained and he said not so much in the proper shops in the souks, but always at the market stalls.
You will be asked by almost every single stall owner you pass to have a look at what they're offering, which can get a bit of a pain, but they don't take offense if you just ignore them and walk past.
If you are a woman, I would strongly suggest covering your arms and at least down to your knees. I had long trousers on and a vest top with a shirt underneath (it wasn't overwhelmingly hot as most of the souks are in the shade) but a lot of other tourists were wearing inappropriately short shorts and low cut strappy tops. This offends a lot of the older Moroccan men, and it will attract unwanted attention from the younger ones - they make no effort to hide the fact they're staring at your chest and I often felt uncomfortable.
However long you are in Marrakesh for, you should definitely visit the souks - you won't have experienced Morocco until you have, and there are some really nice items to buy!
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