eBay is a great place to buy almost anything imaginable, but there are some things you might want to think twice about buying there for safety reasons. This goes for goods with a high rate of counterfeiting or goods with similar attached issues. There is also a group of things that may not be eBay-friendly even if they're not illegal in any way or forbidden by eBay, and you'll find sellers happy to sell them to you.
Don't think of a list like this one as a series of hard and fast rules, but as a risk-benefit calculation. Yes, you can buy them on eBay in many cases, and you'll probably get a fabulous deal (which is often the very reason for seeking them out on eBay). But before you purchase items from one of these general categories on eBay, you should ask yourself whether it's really worth the risk.
Food Items, Spices or Other Consumables
Sure, you can buy things like bulk coffee, artificial sweeteners, spices, candy, food coloring and other things that you regularly put into your body on eBay, but on eBay they're often sold in bulk from sellers whose backgrounds you don't really know, even if they have great feedback and nice About Me pages. Maybe the products are great, but maybe they're seconds, salvage, or imports of lower quality or diluted or cut down in some way. Do you really want to risk putting unknowns into your body?
Supplements or Medications of Any Kind
The same goes double for anything medical or of health care purposes/uses. Here it's not just danger or contamination but also quality and need that's an issue. When your health is depending on the goods that you buy, you want to be very sure they're top-shelf and not "settle for it" goods in some way.
Equipment to Be Used for Health or Medical Care
Medical equipment is expensive and hard to find, but eBay probably isn't the best place to buy it. Sure, you might get a fabulous deal, but you're also unlikely to be coverable by warranties or liability protections, even though in many cases you'd be getting used gear of unknown remaining lifespan. Even if cost is an issue and you're determined to buy used, you're probably better off sticking with local suppliers for medical equipment of most kinds.
Anything That Needs to Be Sterile
Lots of different sorts of things, from eye and face care products to baby care goods are typically sold as sterile at retail—for good reason—and most of their consumers would generally prefer that they are sterile. Because goods on eBay are often sourced through alternative channels or from alternative suppliers, their sterility may be less certain than that of items found at your local chain drugstore and the limits of their liability far lower.
Care or Maintenance Products for Expensive Items
It's great to buy tools, consumables or other care items for jewelry, collectibles, antiques, technology items or even cars to avoid expensive cleaning or maintenance costs when done by third parties. But only you can decide whether it's a good idea to make an item that cost thousands of dollars item vulnerable to tools, supplies or goods bought on eBay at discount rates. For very valuable items, it might just be a good idea to invest in very high-end care.
Critical Parts or Components for Expensive Items
It's also true that you can buy parts for many kinds of expensive mechanical, technological, or other kinds of goods on eBay, but if the item you're repairing needs to work reliably and predictably and/or its value is very high, it's generally good to return to manufacturers or specialists for parts and components rather than sourcing them from quarters unknown.
Non-Branded or Used Goods for Important Needs
There's a lot of off-brand, white-box, generic and used stock on eBay. Most of the time that's fine, but in some cases, you ought to think twice before going the "cheap route," even if it's not a life-and-death situation. Do you really want a generic import box holding backups of your critical data?
Do you really want to pay the labor costs to replace the expensive catalytic converter in your car if you don't know that the replacement will last just as long and perform just as well? Only you can decide whether an item that may be from someone cleaning out their house is right for your important need.
Used Items That Will Be Dangerous if Kept in Bad Repair
Power tools, infant and baby toys and furniture, scientific equipment and other kinds of goods that grow increasingly dangerous as they descend into bad repair or approach the ends of their lifespans are probably not a good choice for eBay purchases since in most cases you won't have an authoritative history of the item or its true (i.e. internal or structural, rather than superficial) condition.
Items That Have Been Recalled
It's true that some people are loyal to goods that later get recalled, suspecting at times that the recalls display an overabundance of caution or that the recalled items "aren't dangerous for someone like me" for whatever reason. It's also true that many of these make their way onto eBay.
But in general, when something has been recalled by a manufacturer working in tandem with government agencies, it's because someone, somewhere thinks that safety and/or liability are a problem. This ought to make you think twice before going to eBay to get that item that "can't be had anywhere else any longer."
Status Items or Critical Gifts
Items whose origins, quality and/or expense are a big part of their value and function are probably not best purchased on eBay. If you're buying something mostly for status and prestige purposes or to impress someone (whether we're talking jewelry items like a high-end luxury watch or engagement rings or something else), saying that "I got it on eBay" probably just isn't going to do the job.
Even though eBay is a perfectly good place to buy a great many great things, there's still a bit of a cultural assumption out there that eBay is a place for saving money and buying goods that are either "alternative" to name/mainstream brands or that come from "alternative" suppliers or manufacturers.