Match the specs to the work
Choose a laptop for the software you'll actually use. Documents, browsing and video calls need far less than video editing or gaming. The processor series name alone isn't enough: what matters is the full model number and generation.
Check how much RAM it has and whether it can be upgraded. An SSD feels much faster day to day than an old hard drive, but look at its capacity and the condition of that particular drive too. Compare the full configuration, not just the brand.
Check battery life and ports
Battery wear affects working away from a socket. If the description gives no remaining capacity or tested runtime, don't take the manufacturer's figure for a new device as the result for this one. Also find out whether a charger is included and whether it is the right one.
For the screen, look at resolution, even brightness and visible defects. If you'll use an external monitor, check for the video output you need: USB-C ports that look the same don't always support the same features. Check the keyboard layout and the condition of the ports.
Before you buy
Find out the operating system and licence status, any account or BIOS locks and how far it was tested. Compare laptops on the same parameters. A laptop with a fuller test report lets you judge the risk better than one that just says «works».