A 16gb would go within a day or two at $425, maybe $450 if you catch the right person.
I see people who list them at $500 firm and they have a hard time selling and I'll notice their ad is still up a week or so later and they've bumped it everyday.
One tip, always list your phone for $25 more than you'll take. People always want to feel like they've gotten a bargain so they'll almost always ask if you'll take about $25 less. Jump on that.