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 itself 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.
I would go so far as to say this applies to anything, really. If you want something from me, odds are decent you’ll get it for the asking – depending on what it is, obvs – but it doesn’t hurt to come prepared.
That said.. just because I ask you to make an offer, doesn’t mean I’m going to make you pay up; but it doesn’t mean I won’t, either. Making an offer and then refusing when I try to collect means you not only lose the game, you lose the chance to play again.