I have a 12" Powerbook with a 1 ghz G4 processor, 512mb, 40 gb, combo drive, tiger. Only about a square inch of the top case has some noticiably scratches. Can any one tell me what a selling price would be for it?
Based only on what you've written here, I'd guess somewhere around $600-$700. It seems like (at least on MR) everyone's been trying to get rid of the 12" PowerBook since the MacBooks have been released. I was thinking about jumping on that boat, but I think I might keep my PowerBook for use when I just need to surf the web, write papers, listen to iTunes, etc. Then, I'll get an iMac as my primary computer. But who knows. I love my PowerBook, and as of now, I'm glad I haven't gone with the MacBook.
Anyway, back on topic. Since the MacBooks have come out and start at only $1100, it's going to be tough to sell a less powerful, used notebook for anything close to that. I've seen top of the line 12" PowerBooks with AppleCare remaining go for $900-$1000, so I wouldn't expect to get more than $700. If you do decide to sell, I'd try eBay, as (in my experience) prices there seem to be inflated a fair amount.
The best way to determine the market value for any used Mac is to search eBay for it, then click on the "completed auctions" box. Based on recent discussions about the value of 12" PowerBooks, I'd estimate a resale value of $450-550 for yours, depending on condition and completeness.
Those 12" Powerbooks are still selling for more than they should be. In Australia, a MB with educational discount costs around $1550 AUD. I got my 12" PB for $2000 AUD (educational discount as well). However, it's 3 years old, has scratches, and a dead battery. I might still get $800-850 or something for it. It's on eBay right now with 2 days remaining on the auction, and I'm going to get at least $610 for it. I expect more than that, of course.