1. Battery wear
Every battery reports two figures: the capacity it was designed to hold, and the capacity it actually holds now. The gap between them is the wear.
A 45 Wh battery that now holds 27 Wh has 40% wear. That laptop does not have “slightly less battery life” — it has roughly 60% of the runtime it shipped with, and the decline continues.
Also ask for the cycle count. Under 300 is light use. Over 800 and the battery has done its life regardless of what the wear says today.
2. Disk SMART
This is the one a fresh Windows install cannot hide. The drive keeps its own log, and reinstalling the operating system does not touch it.
Three things in it matter:
- Power-on hours. Divide by roughly 2000 for years of ordinary use. 20,000 hours on a “barely used” laptop is a story that does not add up.
- Reallocated sector count. Zero is what you want. Anything above zero means the drive has already found bad areas and moved data off them. A number that is climbing is a drive on its way out.
- Pending sectors. Should be zero. Anything here is worse than reallocated — these are areas the drive cannot read and has not been able to fix yet.
A disk can pass every “is it working” test and still be days from failing. SMART is the only thing that tells you in advance.
3. Thermal throttling
On a shop counter, idle, every laptop runs cool. Dried thermal paste and a fan packed with dust only show up under load — and then the processor quietly drops its clock speed to avoid cooking itself.
The test is simple: read the CPU frequency, load every core for ten seconds, read it again. If it dropped more than about ten percent, the cooling cannot keep up.
A machine throttling 30% is giving you two thirds of the speed you are paying for. The fix — new paste, a fan clean — is cheap if you know before you buy and annoying if you find out after.
4. When the operating system was installed
This is the one nobody expects, and it is the one that catches people out.
A machine wiped an hour before you arrived looks brand new. But the install date, the number of user accounts, the last logins and the reboot count all say what actually happened. So does the BIOS release date and the manufacture date on the board.
There is nothing wrong with a seller reinstalling Windows — a careful owner does exactly that. What you are looking for is the gap between the board's manufacture date and everything else. A 2019 board with a two-hour-old install and one user account is not a lie, but it is a question worth asking out loud.
Actually reading them
Most of these need administrator access and a handful of system tools, which is not something you can do politely on somebody's laptop from a browser.
Zyv-Scan reads all four and about a hundred other values, then explains them in plain English or Urdu. It is free, runs on Linux and Windows, and takes about a minute. Put it on a USB stick and take it with you.
Whatever tool you use, run it before you hand over money, not after. Every number here is a negotiating position, and it stops being one the moment the laptop is yours.