Track Lighting LED bulbs flickering
That's very common.  Dimming LEDs is a rather complicated business, due to the need to interoperate with old style dimmers. 

Older dimmers were designed to be retrofit into old-style "switch loops" where there is not a neutral.  The dimmer itself needs a small amount of energy to power itself.  The way that happened was by "leaking" a tiny amount of power through the circuit, which worked just fine with old style incandescent bulbs. But this sometimes confuses the electronic power supplies found in LEDs. 

Quality problems with LEDs occur in three areas: 
-  Electronic power supply (driver) operating life, particularly, capacitors
-  subtle and complex functions like dimming
-  physical build quality (the plastics falling apart or breaking)

eBay products generally fell off the back of a truck in Shenzhen, China, are unvetted for quality, and the manufacturer saved about 25 cents a unit making them as cheap as possible.  On 4 million units that's a million bucks.  Because of the capacitor issue, you can expect disturbingly short service life from these LEDs.  When that happens, don't blame all LEDs generally, blame that brand.  Quality ones will last 10-30 years.  I like General Electric, Philips or Ikea.  I avoid Lights of America, Feit Electric, Utilitech, or any big-box store house brand.