While there are obvious exceptions, the old adage that you get what you pay for still holds. Yes, you can get great bargains on eBay. I have. But what you're often not paying for is quality workmanship, customer service, and humane working conditions for those whose labor you're buying. That is not to say that you can't end up purchasing exactly the same item at a substantial markup from a brick and mortar store or a name brand online retailer, of course. And sometimes that difference represents nothing but "mark up." But the next time you're tempted to go for a deal that looks too good to be true, consider...
() even if the photo appears to be the "same" as a more expensive item, that may only mean that the eBay photo doesn't reveal the differences. Or it may simply mean the retailer has inserted a photo of a more expensive item than they're actually selling.
() if you aren't happy with the quality of the item, do you really want to return it to a company you've never heard of located (if you can determine) halfway around the world? From a company that has not built into their business model the cost of customer service? From a company whose ad suggests that English is not a familiar mode of communication?
() whether there is any benefit in having brick and mortar retailers in your local area. A local merchant has to pay for sales people and a retail location. Is there any benefit for you in having your neighbors employed? In having a place where you can see, feel, and touch the real item?
() whether you benefit at all from paying sales tax, something you'll probably have to do if you buy locally or from some internet retailers. Is there any value in your local schools? Would you be better off with even less educated fellow citizens? Fewer police? Less fire protection?
() whether you care at all about the working conditions of those who produce the consumer items you purchase. I've regularly purchased computer bags from a merchant in San Francisco who manufactures them in that city. Yes, their items carry a premium price in part for that reason. On the other hand, I actually care that working class people in SF are able to make a living and contribute to the life of that city. And I know that the quality of their workmanship reflects something other than an effort to keep costs to an absolute minimum.