All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
When a tour guide agrees with some shops and restaurants to bring tourist groups against a specific commission, this is a form of brokerage, and in Fiqh terms, it is called "Ji`alah" {Conditional payment}. In "Ji`alah," it is permissible that the wage is a specific sum or a percentage on which both parties agree. However, the following matters should be taken into account:
First: This is should be done in the form of advice to the tourist groups. In other words, the guide should take them to trustworthy clean shops and restaurants which offer the best products and services for appropriate prices. Thus, the guide shouldn`t be unjust to the tourists by making them pay more than the regular prices in order for him to receive the highest commission possible.
Abu Hurairah (May Allah be pleased with him) said: The Messenger of Allah (PBUH) said: "He who takes up arms against us is none of us; and he who cheats us is none of us."
[Muslim]. Narrated Umm Salamah: "The Messenger of Allah (PBUH) said: 'The one whose council is sought is entrusted." {Tirmithi}. The Messenger of Allah (PBUH) also said {What means}: "Selling a commodity to someone-who doesn`t know the actual price-for higher than its regular price is injustice." {Bayhaqhi}.
Second: What the guide does should be authorized by the touring company he works for. Moreover, a guide is an employee who acts on the orders of his employer and in his best interest. And Allah the Almighty knows best.