When selling into a forum like this one, I think a lot rides on your established reputation. A well-respected member of some years will "get away" with asking for closer to retail pricing of goods, a new member promising the moon will be looked on skeptically and may have to go to ~20% pricing to get people to take the risk.
You, being the former, should be able to get 40-50% of new street prices, maybe more with the right product or desirability. But it's so variable - is the person in need looking at FS threads that day? How patient can you be??
I'd also suggest tempering rapid "$450", then "OK, $400?", etc adjustments on something. Too quick, to often and people will just know to wait, even if the initial price was quite reasonable.