What's the difference between a mint used unit and a new one? The basic architecture for many units has not changed, but the inflation went up, at least in the US. Perhaps 10% off the new unit price is a bit dreamy, but ~20% is quite acceptable.
What you are saying here is a typical conventional wisdom, so I can't just disagree with it...
But why buy a used one with tens or hundreds of hours on it, when you could get a brand new one, never used, direct from factory with full warranty and support, any new updates, completely un-breathed spotless clean throughout (lungs and hoses, DSV, fittings etc), never been wet, better resale future value, and front row status for only a 10% to 20% premium?
60% of retail would be more realistic starting point for anything properly used, maybe 80% if it is less than 50 hours. I guess some advantages could be convenience, not having to pay tax on it, being able to buddy up with the seller/do them a favor, depending location/circumstance.
Owners/sellers like the dream that it looks/operates the same as when new, then it should be tradable for near equal what we paid. But it is a depreciating asset, in an evolving market. Owners got 10s or 100s of hours of use out of it--you don't get that for free. The warranty is over. Longer-term issues now have a head start. Future resale on this unit will now be lower, for the new owner. The clock has already ticked for a year+ (or five years) on long-term support, availability of parts, current instructors, and compatible, fresh dive buddies. The [
expensive] computers are probably outdated now, versus ones you get with a new unit.
The "like new" logic is a fallacy for above reasons. Sellers just thinking about themselves. Wise buyers shouldn't buy that.
The buyer is comparing prices between used units. Not your unit versus its original retail price.
I have seen instructors/reps sell used same-year units at or near retail. But they can do this because they brought the unit somewhere--like in a remote country--and here it is, yours today, with no easier way to get a 'new' one quickly. In that case, they are actually offering something unique to the buyer.
If there are many more of these 'mint' 3-5(+) year old rebreathers for sale than there are actual buyers, that pushes prices down for anyone committed to sell. Sellers could list at $8k and refuse lower offers all year and earn nothing, or just take one of the ~$4k offers and be done with it, $4k richer today.
If 50% of current rebreather divers buy a new rebreather, and they all try to sell their old one, there won't be enough buyers at $5k+ for all of them. Either the prices come down, or there are a ton of "no sale" and people stuck with multiple units. Whoever is most motivated to sell is going to set the used market price.
The upshot is, the user base needs to increase. If overall sales go up, producers sell more new units, the people lusting for upgrades pony up a net ~$5k+ ante for that, and their older units go at a realistic discount (like half off original price) to people who would love to get into the game for like $3-4k all-in. Ready-to-dive, screw this new "price before computers" nonsense (Kiss Sidewinder was playing that BS, if I recall)