Agree with so many posts here.
Selling "new unused" for 75-90% seems reasonable, if it's not popular it won't sell and I think that's the major factor across the board, you can ask for anything you want, it doesn't mean you'll ever get it. You may annoy your potential customers so much that then you are labeled difficult to deal with and you end up never selling or time goes by and it's way less.
I think a bunch of this "it's worth x" stuff is typical High School concepts of valuation and the other is just honestly not knowing.
Just roll your eyes, have a laugh, and move on but don't be afraid if you actually want the item to say what you think about the value.
I found a pair of Atomic DH's on ebay one day $1000!?! They were from the Beta4 era. I contacted the seller since the description was totally wrong too and said, "I'm guessing you got this in a yard sale and have no clue what it is". That started a conversation about how this was part of a lot sale at an airport for unclaimed luggage. I told them I know they are huge and heavy, go to UPS figure out what it costs to send them and I'll give you that + $100. They were happy for it. They had no idea Atomic DH 215's were not something that like everyone was using. When I got the skis it was obvious it was a ski team ski that was traded around on the FIS circuit. That's not uncommon for those that only enter an event occasionally. It had no value for any current competitor but it's not like these things grow on trees and $100 + shipping was fine to me. They probably have 4-6 comp weekends on them.
Not to belabor the HS aspect, but I remember this math and thinking because I had it too in HS!
If the retail number is $1000 then the used number is 80% of that. You see this on car forum sites too and there people are under the impression that adding $1000 in wheels makes the car worth $2000 more or their car is a classic (there's actually a real definition for what is a classic and it's not "I think it's cool and did a bunch of mods")
So here's the quick lesson:
Any asset which is consumable always depreciates from a practical stand point. Keep that in mind and you win every time when propositioned for anything new or used.
From a business stand point ALL assets depreciate, that's how accounting actually works. You may realize a gain on the asset when you sell it (called disposal) but all assets are technically depreciated from a business stand point and there's actual rules, formulas, and methods for that, some come from the IRS.
Occasionally you get some glitches, you happen to have an unused pair of skis that has a cult following and it's 10 years old and there's few known to exist. You end up with a collectible car (and don't drive it like ever). You buy something and use it a little bit, skis, and there's no more supply for the year or ever (Hart skis) or costs go up and someone happens to need it so they pay you back retail or even a bit more. All those are glitches and not normal reality.
IMO below assumes used/mounted not "unused but old"
Ski boots? Used plastic and foam? Very high depreciation and low useful life to begin with. Don't bother anything > $100-200.
Skis? Kinda depends, park skis, post 30 days probably very low, rarely used powder skis with 2-3 runs on them better
Poles? Who cares
Bindings? Better than average if not > 5 years old probably about 25-50% of retail.