These are 285 rules that the Ferengi live by. I have compiled a list from several books and have listed them here. A few have been omitted because of content, but this is a fairly complete list through the fourth season of Star Trek: Deep Space Nine.
1. Once you have their money, you never give it back. ("The Nagus")
3. Never spend more for an acquisition than you have to. ("The Maquis, Part I") [OMNI]
6. Never allow family to stand in the way of opportunity. ("The Nagus")
7. Keep your ears open. ("In the Hands of the Prophets")
9. Opportunity plus instinct equals profit. ("The Storyteller")
10. Greed is eternal. ("Prophet Motive") [OMNI]
16. A deal is a deal ... until a better one comes along. ("Melora")
18. A Ferengi without profit is no Ferengi at all. ("Heart of Stone") [OMNI]
19. Satisfaction is NOT guaranteed. ("Meridian") [ST30]
21. Never place friendship above profit. ("Rules of Acquisition")
22. A wise man can hear profit in the wind. ("Rules of Acquisition")
31. Never make fun of a Ferengi's mother. (The Siege")
33. It never hurts to suck up to the boss. ("Rules of Acquisition")
34. War is good for business. ("Destiny") [OMNI]
35. Peace is good for business. ("Destiny") [OMNI]
47. Don't trust a man wearing a better suit than your own. ("Rivals") [OMNI]
48. The bigger the smile, the sharper the knife. ("Rules of Acquisition")
57. Good customers are as rare as latinum--treasure them. ("The Armageddon Game") [OMNI]
59. Free advice is seldom cheap. ("Rules of Acquisition")
62. The riskier the road, the greater the profit. ("Rules of Acquisition", "Little Green Men" [ST30])
75. Home is where the heart is, but the stars are made of latinum. ("Civil Defense") [OMNI]
76. Every once in a while declare peace. ("The Homecoming")
102. Nature decays, but latinum is forever. ("The Jem'Hadar") [OMNI]
103. Sleep can interfere with ... ("Rules of Acquisition") -- Pel is interrupted before he can finish quoting this rule. [OMNI]
109. Dignity and an empty sack is worth the sack. ("Rivals") [OMNI]
111. Treat people in your debt like family -- exploit them. ("Past Tense, Part I") [OMNI]
194. It's always good business to know about new customers before they walk in your door. ("Whispers") [OMNI]
203. New customers are like razor-toothed Greeworms. They can be succulent, but sometimes they bite back! ("Little Green Men") [ST30]
211. Employees are the rungs on the ladder of success -- don't hesitate to step on them. ("Bar Association") [ST30]
214. Never begin a negotiation on an empty stomach. ("The Maquis, Part I") [OMNI]
217. You can't free a fish from water. ("Past Tense, Part I") [OMNI]
285. No good deed ever goes unpunished. ("The Collaborator") [OMNI]
286. (Quark's Rule)When Morn leaves, it's all over. ("The House of Quark") [OMNI]