You're going to want to do some hands-on testing. So, let's say you decide to ignore my advice and buy a machine from a local seller. If a seller doesn't give you any details before you see the machine, avoid them. It will generally give you model year information as well as some other details. If you encounter a seller who claims no knowledge of the model, ask for a serial number (it's available on the unit or in the About this Mac dialog under the Apple menu), and then run the number through Apple's Check Coverage page. I spoke to several sellers who claimed they had no idea. One of the problems with Craigslist, eBay, and Facebook sellers is they often won't specify the year of the machine you're buying. Apparently, Gmail also checks the OS version. Even when using other browsers, Gmail wouldn't work. I got hit with Chrome not upgrading on a too-old machine. I reached out to OWC, which sells refurbs, and it told me a lot of folks are running somewhat older OS versions. See: Which Mac to buy? 10 tips to help you decide If you see inaccuracies in our content, please report the mistake via this form. If we have made an error or published misleading information, we will correct or clarify the article. Our editors thoroughly review and fact-check every article to ensure that our content meets the highest standards. Our goal is to deliver the most accurate information and the most knowledgeable advice possible in order to help you make smarter buying decisions on tech gear and a wide array of products and services. ZDNET's editorial team writes on behalf of you, our reader. Indeed, we follow strict guidelines that ensure our editorial content is never influenced by advertisers. Neither ZDNET nor the author are compensated for these independent reviews. This helps support our work, but does not affect what we cover or how, and it does not affect the price you pay. When you click through from our site to a retailer and buy a product or service, we may earn affiliate commissions. And we pore over customer reviews to find out what matters to real people who already own and use the products and services we’re assessing. We gather data from the best available sources, including vendor and retailer listings as well as other relevant and independent reviews sites. ZDNET's recommendations are based on many hours of testing, research, and comparison shopping.

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