Buying something used vs. new is a classic way to save money. Garage sales and thrift stores are standard for this type of commerce. But these days, thanks to apps and the internet, there are dozens of ways to buy treasures sellers want to get rid of. There are a few rules of thumb for effective 'treasure hunting.'

1. Explore the Uncharted Territory

Before you start buying, get familiar with the ins and outs of the site you are visiting. Some sites, like Etsy — where you can not only buy handmade items, but used items as well — are pretty straightforward. EBay can be a bit more complicated, with its variety of options for buying and selling and tricks to scoring the best stuff. Their Bidding and Buying Help page can help you get the lay of the land.

2. Read the Fine Print

Before making a purchase, form a solid understanding of important details like shipping fees, shipping times and return policies. The information should all be accessible – read it so you know what you're getting into.

3. Be Discerning

From the old guard like Craigslist to newer players like local re-selling marketplace Wallapop, most of these sites offer seller ratings or reviews. They are all a little different. But before you buy from someone, try to figure out if this person is reliable. Look for top-rated sellers with reviews confirming quality merchandise, responsiveness and fast shipping times.

4. Look for a Quality Guarantee

While it's pretty much a free-for-all on most of these sites, with sellers posting and selling their wares with no oversight, some sites, like clothing and accessories re-seller ThredUp, hand-select the merchandise on their site. If an item is less than perfect, the imperfection is indicated so you really know what you're getting.

5. Know You're Not Alone

Buying items from individuals may be unnerving, but most of these online marketplaces have protections in place to ensure you are a happy customer. A good example of this is clothing marketplace Poshmark's Poshprotect, which does not release your payment to the seller until you give the A-OK. And if you're unhappy, they make it fairly easy to return your order (it has to be for a good reason, not just because you changed your mind). Local re-selling marketplace OfferUp offers an extra layer of security with its TruYou verification system, which helps to ID the seller as a "trusted" user.

6. Meet Face to Face & Do It Safely

If you see something you like on a local re-selling marketplace like Craigslist or competitors LetGo, OfferUp and Close5, be sure to meet the seller somewhere secure – you are meeting a stranger after all! Some communities offer designated Craigslist sale zones outside fire or police stations specifically to ensure the safety of these face-to-face sales. You might consider bringing someone with you, and if that's not possible, let someone know where you will be and when you expect to be home. Also, do not buy anything until you have thoroughly looked it over and tested its functionality.