Question about Halides

[Eyford01]

I recently bought a set of 250w metal halides, the old bulbs were supposedly 14K and looked great but were over a year old so I ordered a new set of bulbs off ebay which has produced good results in the past but these new bulbs which are supposed to be 15k are very yellow and constantly flicker. Never had this problem when replacing halides, are they just crappy bulbs or is there a break in period or what? Anyone have any idea what might be going on?