Short answer: yes, almost always, and usually for more than you would guess.
A modern iPhone that will not power on is still a collection of valuable, working components in a housing that somebody wants. The screen alone, if it is intact, is worth a meaningful amount. That is why a dead phone is a price rather than a refusal.
First, try these, in this order
A surprising share of phones that appear dead are not. Work through this before concluding anything.
- Charge it for a full hour on a known-good cable and a wall plug, not a laptop port. A deeply drained battery shows nothing at all for the first several minutes.
- Try a different cable and a different plug. Cables fail far more often than phones do.
- Force restart: volume up, volume down, then hold the side button until the Apple logo appears. Hold it longer than feels reasonable, at least twenty seconds.
- Clean the charging port. Torch, then a wooden toothpick, gently. Compacted pocket lint is one of the most common causes of a phone that will not charge, and it looks exactly like a dead phone.
- Plug it into a computer and see whether it is detected, even if the screen stays black. If it is, the phone is alive and the screen is the problem, which is much better news.
If it stays dead, do not have it repaired first
This is the mistake that costs people money. A diagnostic plus a repair on a phone you are about to sell almost never returns what it cost, and an aftermarket part can lower the offer below what the unrepaired phone would have fetched.
Sell it broken. The price already accounts for the fault.
The Activation Lock problem, and how to solve it blind
This is the one thing that genuinely can make a dead phone worthless. If it is still signed into your Apple Account, nobody can do anything with it.
You do not need the phone to fix this. Sign in at iCloud.com on any computer, open Find Devices, select the phone, choose Erase This Device, and then Remove From Account. It works whether or not the phone can switch on.
Do this before the courier collects it. A dead phone with the lock released is worth real money. The same phone with the lock still on is worth nothing to anybody.
What it is actually worth
It depends almost entirely on which parts survived, and that is not something you can determine from the outside. A phone that took a knock usually has an intact board and a broken screen, which is the good version. A phone that got wet often has the opposite problem.
Water damage is the harshest single fault, because it spreads and because it can surface months later. Declare it even if the phone worked afterwards. Apple's internal moisture indicators tell us anyway, and a declared fault is priced while an undeclared one becomes a phone call.
The short version
Charge it properly, clean the port, force restart. If it stays dead, release the Activation Lock from iCloud.com and sell it as it is. Do not repair it first. A dead recent iPhone is worth a lot more than a working ancient one.