My understanding is also that most discount codes are restricted to members of the relevant groups. For example, while anyone who knows the URL for our corporate travel site could obtain the codes for our car rental packages, when using them I have always been asked to show my ID card as proof of qualification. Similarly, our airline discounts are only internally distributed, and always with a notice that outside distribution constitutes breach of contract.

Note that some codes are more openly distributed, or at least available to groups with open membership, so in many cases this issue is in fact moot. For example, SmarterLiving (http://www.smarterliving.com), which compiles bulletins with all of the last-minute fare specials by city of origin, also has negotiated rates with Alamo and a special fare deal with IcelandAir. Any subscriber to a SmarterLiving newsletter (free) has access to these. Similarly, various other loosely defined organizations have discount codes, such as for car rental--AAA, my bank, various credit cards, etc.

From discussions with the President of SmarterLiving (a friend of mine), I understand that discounts increase as one can draw on a larger customer base. For example, the SmarterLiving disount with Alamo recently increased, as SmarterLiving crossed a threshold number of subscribers. Thus, JIMBOLIGUY's suggestion of a discount group may not in fact yield the desired results, at least to start.