Surely someone here knows the answer to this ... I've been wondering about this for a while now.

Car rental and hotel discount codes/group codes ... how do they work and how are they negotiated?

My company has a code with Avis that I can usually get a pretty good rate with (20% off or so), but today this was posted in the Avis thread:

http://www.flyertalk.com/forum/Forum77/HTML/000005.html

I just tried this code for a rental I have coming up in NYC next month, and this code got me a rate $16/day less ($57/day vs. $73.20 for a Premium car).

Is it against the rules or unethical to share these codes in this way and use them even if you aren't really affiliated with the group they come from?

I'm more interested in hotels actually ...

Don't some companies have negotiated rates with the large chains? I'm thinking if I can find someone who works for a company with a negotiated rate at Hyatt or Marriott, couldn't I just use their group code (as long as it's not direct billed of course), and wouldn't this actually be advantageous to the company since they can/do probably get better deals the more they stay at the chain?

For that matter, how do the negotiated rates work at all ... could us Flyertalker maybe form some sort of membership organization and maybe get negotiated rates with hotel and/or car rental companies? How about the FF Addicts Club?