From the article "Helpful Hints for Dealing with Martian", in the March 2005 issue of Alien Invasion Quarterly:
If, say at a party or something, I have something you want - some bit of kitsch or whatever - which is obviously of little value to me, and I tell you to make me an offer.. seriously, just make an offer. If it really is of no value to me, odds are the offer alone will be an adequate price. I just want to see what kind of offer you'll make. Mind you, you should be serious and sincere in your offer, 'cause I might accept it. But, despite intentions to the contrary, I tend to be at least somewhat reasonable in what I expect someone to give for something I don't care about. In the worst case, I'll tell you your offer is boring and make you come up with something better.