Credit card companies and merchant agreements

What, exactly, are the responsibilities of merchants with regards to accepting credit cards?

I know that they have to abide with agreements from the various credit car companies. Can I see a copy of those agreements, or do they vary by merchant?

Are there any applicable laws that merchants have to stick to as well?

I did a bit of searching (SDMB and Google) and came up with this:

Anyone have more specific information?

I thought that were actually required to ask for a photo ID. I think maybe if that was forbidden in the past, it’s been changed, because they’re doing it all the time now. And that’s a good thing.

I’ve also read that they’re not supposed to require a minimum charge, although lots of liquor stores and bars do that (not that I know anything about liquor stores and bars).

Also, while it’s not OK to charge more for using a credit card, it is OK to give a DISCOUNT for using cash. Stupid, yes.