Keep your Mac, and fix the problem.
Which Mac do you have? How much RAM? Are you running a lot of applications or large files at the same time?
I can just about promise you, your Mac is fine, but the user might not know what they're doing.
For example, are you shutting off the application correctly? On a Mac, you have to "Quit" the application. Clicking the window closed doesn't shut down the application. Look in the dock, how many little icons have a small black triangle under them? It means those applications are active. Too many, and if you don't have enough RAM, it will bog down.
Open your disc utility, and do a permissions repair.
But from what you're describing, you don't have enough RAM, and are running too many apps at the same time.