Well, I went looking all over the net and there are tons of sites the tell consumers how to initiate a chargeback, but very, very few that cover the merchant side. The best I could come up with is the following from the Maryland Attorny General's office at:

http://www.oag.state.md.us/consumer/tip37.htm

"Also, the merchant has the right under the law to try to collect from you directly or take you to court--even if your card issuer grants the chargeback."

That was dated 1995. I did find a mailinglist with a bunch of merchants complaining in 1997 that the federal laws, particularly the Fair Credit Billing Act (FCBA) make it way too easy for a fraudulent uses of chargeback, and in all their discussion no one mentioned suing the consumer directly. I tried reading the FCBA but it is total lawyerese and thus meaningless to the layman. One item that I got from a couple of places is that the FCBA tends to override any state laws (particularly for inter-state disputes) except when the state laws are more pro-consumer (the common example is that the FCBA allows only 60 days from statement date to dispute, but if the local state law allows 90 days then you get the extra 30 days automagically).