I have had HID kits in all my cars since 2000 and 90% of them have been from eBay. Any HID kit can have issues no matter what manufacturer it is or from who you buy it from. The number 1 culprit is the installer failing to put a relay on line for them. The ballasts are very sensitive to voltage and if it has variations in voltage or not enough voltage, the ballast WILL eventually fail. That is why you get flickering, one light wont turn on, you have to turn them on and off to get them to work, and finally a failed ballast or bulb. Since 2001 I have easily had 30 sets of HIDs and multiple failures, I learned the hard way buying new kits all the time until I figured out that they needed to be installed with a decent relay. Im not saying you wont have issues with a relay because most of these manufacturers have poor quality control. As long as you buy from a source that is willing to work with you if you have an early failure. Newer cars will also need a capacitor along with a relay kit because the computer will think that your bulb is out and light up a fault.
Now for the light housings (plenty of these under my belt too having owned 10 G-body cars). These also can be tricky because they tend to not seal right and you get moisture in the enclosure if not sealed correctly. As far as I know there are a few types of enclosure i.e.. projector type, non-projector, plastic lens, glass lens, H4 bulb, and 9006/9007 bulb. Glass is what you want because the plastic will fade and turn yellow, personally I prefer the look of the non-projector, and finally the ones that seal the best are the 9006/9007 bulb type housings. So if you find housing that are glass and 9006/9007 type bulbs you wont have to worry about fading issues or moisture if sealed properly.