For trading, 3/4 of the top end value is my rough standard. If the recipient is being generous, I tend to reflect that back. If they're being a little "overly optimistic" then I'll stick with my standard pricing.
Remember that certain times of year skew eBay prices dramatically. Always check the sale date on sold listings, as I think it covers 90 days. Pre-holidays, pre-major events, etc push things way up, and for some reason school holidays occasionally lay waste to any attempts at selling.
For sales, depends what I'm after. For a fast sale, middle of the road pricing, making sure
what I take after fees is worth it. If I have a stash of stuff, in no hurry to sell, and a little trickle income would be nice, I price upper end and put them on a month-long listing.