Authorized refurbishers typically sanitize, sort, and grade the units based on physical look and functionality. They thoroughly test each system, looking for damaged components, battery function, screen quality, power supply, loose connections, hard drive and optical drive. If a seller does not follow a process like this, the product isn't really refurbished - it's 'as is'. Missing or defective components — RAM, graphic cards, capacitors, ICs, hard disks — are replaced and the machine undergoes a complete data wipe. The computer is then tested, cosmetic defects repaired, and a new OS is installed before being packaged for its new home. That last software bit is critical. Some sellers may try to install the original OS and pass it on to buyers, but that would not be a legal license. Certified Refurbishers have agreements with Microsoft to copy properly licensed operating systems (primarily Windows 10) onto refurbished units. After a refurbisher inspects, cleans, repairs and restores a used or returned laptop to factory settings, the unit is certified to be in good working order and made available for sale at a discount.
Be sure you understand what buying a refurbished computer means. Refurbished computers can be anything from a brand new device that has been returned because it was an unwanted gift to a used one that has been in service for years before being professionally refurbished by one of the many companies that recycle electronic products. The typical boilerplate that applies to most refurbished laptops is that they:
If you want a brand new computer that smells like it's just come off the factory line, complete with shrink wrap packaging, then refurbished laptops are probably not for you. If, however, you want a computer with plenty of life left in it that will meet most people's needs and requirements, refurbished may be for you.
Decide how much money you want to spend on your refurbished computer; go for your absolute limit and add an additional 10% margin (that will make sure you don't miss out on bargains that are just outside your limit). Do consider extended warranties which can sometimes be bought at the same time; they offer additional protection should the computer suddenly fail.
That applies to all computer purchases, regardless of whether they are new or not. Make a list of what you need and what you want. Start with the bits you won't be able to upgrade easily like the screen size and screen resolution for a laptop, or the chassis size for a desktop - then think about the processor.
Next, follow on with system memory, hard disk drive, and graphics card, since these can probably be upgraded fairly cheaply and easily. Do you have any brand preferences? Or specific features you need to have (optical drive, wired connectivity, available ports etc)?
After having compiled a list of potential buys, find a store that has what you are looking for, and be sure to look for promotional coupons or sales. Sign up for email notifications if no sales are on currently - It may be worth waiting a short while to get an even better deal!