Here's a trick I learned that I know will be useful to those who are working on portfolios or creating presentations using unedited product photography.
How does it work? Well in a nutshell, you simply select the tool, then select the color from the background using alt (mac the option key) that you want to delete and the eraser will only delete that color.
*Just a warning, this isn't the use all fail proof tool, it will only work so easily if you've shot your product with a consistent background. The results wont be the same if you're shooting your product in say the woods with trees in the background then want it on a white backdrop, that's another much longer tutorial.