There is no "rule of thumb" per se regarding tipping in Morocco. Moroccans themselves might only leave a few dirhams on a 150 dirhams dinner bill. At many of the upmarket restaurants in the tourist areas they will add 10% to the bill, therefore check your bill. If you don't receive good service then don't tip and if you get great service give more than 10%.
In taxis, just round up to the nearest 5 dirhams, e.g. if the taxi meter says 17, pay 20. Though often with taxi's the meter won't be working, so always ask the price or check the meter before you start your journey.
For the bellboy who carries your bags to your room or from your hotel to a taxi, 10 dirhams would be appropriate, unless your bags are extremely cumbersome.
Hotel maids are poorly paid, so if you have had fresh towels and your room cleaned then do leave a decent tip. 100 dirhams for a week's stay would be really appreciated by any maid. Place the banknote inside the pillowcase, then you can be sure that your room maid will get the tip and it won't go to the head housekeeper, who may sweep the rooms on departure day!
The real question for many visitors is "what do I tip someone who has guided you to a place in the medina?". This happens all the time as the medinas can be confusing and the minute you stop to consult a map or look vaguely lost, someone will appear at your elbow to offer to help you fnd the way. First, take all reasonable precautions to avoid this situation. If you are unsure about venturing on your own in the Medina, it is almost always better (and cheaper) to hire a professional guide. Second, take a good look at the person offering assistance. Most often, the "guide" will simply take you to shops before leaving you stranded (but not after requesting a hefty tip). If you must accept, 5-10 dirhams is perfectly acceptable if you are lead to your destination. Keep in mind that a long taxi drive would cost 20 dirham on the counter, and an official guide for the medinas would cost 120-150 dirhams for a half-day tour.
Occasionally, an unofficial "guide" will latch onto you even if you know where you are headed and then try to demand payment for his services. Obviously, you are under no obligation to pay anything. Sometimes a guide will try to take you to the tanneries or wherever else, and even if you assure them you know where you are going, they will tag along behind you and then demand 20 dirhams for "helping" you arrive at your destination.
And what about beggars? Zakat, or the giving of alms, is one of the five pillars of Islam and is akin to the tithe system in the Catholic church. Many Moroccans will give coins to beggars as giving alms brings "baraka" or blessings from God. 1-5 dirhams is a common "donation". If you are not inclined to give (and that's OK too), you can say "Allah yasahel" (may God improve your situation) - or if that phrase escapes you, a smile will suffice. Peristent begging is not acceptable, and once you have refused, if the requests continue, it is OK to ignore them and move on.
