Quality Tested: When you buy a used unit from a quality used retailer, you are assured that the piece has been tested to make sure it is operating at peak performance. The technicians will test each one, identify any problems, and fix the problems. New units are normally just "spot" tested.
A Used Computer Warranty: When you purchase a used piece, the retailer will normally provide a quality warranty. As well, in many cases, the manufacturer warranty will still be valid, depending on the age of the unit. You can often purchase an extended warranty at a reasonable price.
Excellent price: The price of a used one is far less than a new one, often from #100 to a couple of hundred dollars. Prices will normally depend the age of the computer. Generally, the older the computer is, the cheaper the price.
Option of Return: Quality used retailers will offer a set period where purchasers of used computers can return the used computer if they are unhappy with it after they have tried it at home. However, you will not be able to return it if it suffers damage such as spilling liquid on it while in your care.
Less Expensive to Upgrade: Today, there is always new computer technology coming out on the market. After a few months of ownership, a new computer can often become outdated. It is often cheaper just to upgrade a used computer when new technology emerges. Constantly replacing computers with new computers can be really expensive.