I have been on eBay for quite some time already and it is really hard sometimes to stay away from cheap prices for products that come from sellers in Hong Kong, China and some other not that reliable places. One needs to be really careful not to purchase fake items that can even have a hologram and a package like original. 3 major problems with electronics from China that I had was a Sony Duo memory card for my phone, mp3 player and GPS receiver. The memory card that I received worked on some other devices but didn't work on my phone. I contacted the seller and he told that this is a compatibility problem and accepted the return. In this case I lost my shipping payment and I also had to pay for the shipping it back. It was a light item and it didn't cost much.
The mp3 player worked for about 4 months and then the buttons stopped responding, it would turn off from time to time. With MP3 players I can definitely say -- buy it only in the local stores. The last mp3 player that I bought was SanDisk Sansa Clip and I had to replace it with another one because the battery wasn't functioning well. There was some kind of energy leak. It would discharge after a couple of hours of use. After I changed it to a different one, the problem was solved. So, there could be problems even with the branded merchandise and that is the case when you want to make sure you can exchange it or get your money back. Generally if you buy a branded thing, you will have more esthetical feeling (you will enjoy it more), it will last and you will have warranty. How much time it will take to contact customer support and actually replace the defective widgets is another story but at least it is possible and feasible.
With GPS receiver however it is a different story. I paid a price that was much lower than in the stores but it was a non-branded GPS receiver. When I got it, it worked for a couple of weeks and then just died. I have contacted the seller (ebay name: cardmagasin, real name: Yee Yuen Pang) and he told me that I should try to replace the battery and try if it will work. I told him that I do not have this type of battery and I probably should send it back to him for replacement. And guess what -- no answer back. He disappeared and then was no longer registered on eBay. It was a non-branded so I could not go and complain to the customer service or get it fixed. It even might be dangerous since it should send the Bluetooth signals. So, my GPS receiver has to go into the recycler. Here is a picture of what not to buy on eBay:
One very obvious thing to do is to check the feedback of the seller. If there are some people saying that the sold things were not working, fake or similar, do not take the risk. Generally, do not risk buy electronics from eBay. Things like cameras, phones, mp3 players, some of the computer-related hardware should not be bought from unknown sellers from mentioned regions.
I have to mention that I bought quite a few good things on eBay. However all of them are from Europe, US and Japan: a notebook, 3 phones, router, USB Hard Drive, TV Tuner, USB Flash Drive and some others.
Just a note, if you are looking for a good memory, flash drive seller from eBay, I would recommend jjmedia_usa.