"Buy used" is probably the most popular advice given to someone looking to save money, and it's not bad advice — most of the time.

There are three categories of items in the realm of buying used:

Items we never consider buying used. Looking at you, socks and underwear.
Items we don't think twice about buying used, like books, artwork, and cars (provided the car has been inspected).
The items that seem like a good deal but we're not so sure about. That's what we're here to discuss.

1. Bicycle and motorcycle helmets

This list isn't in any particular order — except for this one. You don't want to take any chances with the safety of your cranium.

Helmets are designed to protect you for exactly one crash, and just because a helmet looks relatively new doesn't mean it's a crash virgin. A hairline crack beneath the helmet's visible exterior could be lurking, and while "hairline" doesn't sound serious, it could very well mean the difference between the helmet cracking into pieces and failing or staying intact enough to save a life.

Even if a used helmet looks pristine, pass on it. It's not a risk worth taking.

2. Mattresses

Unless you're looking to colonize bed bugs, don't go searching garage sales and Craigslist for a used mattress.

It's an unpleasant thought, but mattresses are cesspools for bacteria, dead skin, bodily fluids and bed bugs. An infestation of bed bugs can contaminate an entire home, and the cost of extermination will far outweigh the difference between a used and new mattress.

Another thing to consider with mattresses: They typically only last about 10 years, and there's no way of truly knowing how long it was used for if you buy from a stranger.

3. Car tires

Used tires are sold and put on cars with regularity, which is a bit concerning. Like helmets, tires directly impact your safety every time you get in your car.

The problem with used tires is there's no surefire way to tell where or how they were previously used.

Don't just take my word for it — here's what ConsumerReports.org has to say on the matter of used tires:

The tire could have been driven overloaded, underinflated, or to excessively high speed. Any one or a combination of these factors could lead to internal damage not visible from the outside. In short, the used tire could be unsafe.

4. Vacuum cleaners

This one is pretty simple. There's only one reason people get rid of vacuum cleaners: they no longer work well enough to warrant keeping.

Unless you're getting a used vacuum from someone reliable, pass on it and buy a new one.

5. Computer software

Computer software, like Microsoft Office or a game, might seem like no-brainers to buy used. If a disc works in someone else's Mac or PC, why won't it work in yours?

Most computer software comes with an installation code that prevents it from being installed on multiple machines. If the code has already been used, you're essentially buying a paperweight.

If you spot used computer software for sale, scan the box for a code or do a little research online. If it requires a code to install, let someone else waste money on it. Usually, the code can be found on a piece of paper within the software case.

6. Shoes

There's nothing wrong with buying used clothing, but you should pass on pre-owned footwear. Over time, shoes adapt to the shape of a person's foot, which means secondhand shoes will never quite fit properly. This is especially true with running shoes, as the increased impact causes shoes to mold more quickly and drastically.

7. Cookware

Pots and pans can be okay to buy used if they look almost-new, but if they show any visible signs of wear, don't buy. It's impossible to know what kind of chemicals could be seeping out from the scratched-up griddle you saw for $5 at your neighbor's garage sale, so you're better off without it.

coffee laptopFlickr/jonolistA used laptop could be harboring spyware or viruses.

8. Laptops

Few things become outdated faster than a computer. Each year new models are released with updated operating systems, increased memory and sharper displays.

Ok, so you might be thinking, "I don't care if a laptop is outdated — I only need it to check email and use Microsoft Word." If that's the case, consider a few things before buying. One, you don't know what kind of spyware and/or viruses the computer could be harboring. Two, a used laptop doesn't have a manufacturer's warranty. Three, new ones are more affordable than you might think.

Once upon a time — okay, it was around 2000 — the average new laptop went for over $1,400. That's no longer the case. A quick browse through our deals on laptops and you'll see you can score a basic, usable laptop for under $250, and a high-end one (like this MacBook Air) for under $900.

One thing I do recommend is buying a refurbished laptop. Buying refurbished is a great way to save money and be ensure your computer is virus-free and in perfect working order.

Source: http://www.bradsdeals.com/blog