What are you buying?
For items such as tools, refurbished in most cases, is as good as new. Items like power drills may have a new motor, although signs of cosmetic use may be visible, their operation will function flawlessly. On the other hand, items like wood or materials like screws, nails, and small items of this kind, might not always be the best when used or pre owned. So, make sure you know where you are buying these items from as well as guarantees you receive to ensure they will withstand pressure, use and the stresses placed on them.
What are you doing?
If you are building a swing set for the kids, you want the materials to be as solid and sturdy as possible so they are safe. If this is the case, maybe used isn't the ideal solution. On the other hand, if you are staining a coffee table or fixing a small tear in upholstery, items which are pre owned will work wonders. Not only can you buy them for a lot cheaper than the retail price in most cases you can barely (if at all) notice the level of use.
Not every DIY job will allow you to purchase used or second hand items. However, many will. For the jobs that do consider these factors to ensure the items you buy second hand are durable and sturdy enough to complete the job and withstand use.