You can find hundreds of different lighting products for car, home and office on eBay (and elsewhere on the net...alibaba, for example) sold under the CREE name. Cree doesn't make them. Cree very likely doesn't make the LEDs in them. Virtually all of it is counterfeiting and theft of intellectual property (Cree name and trademarks). The use of the Cree name is intended to get people to think "Oh, hey, Cree! That's a good name in LEDs!" and buy.
I've had the pleasure of disassembling some of these devices and found that the ones I've purchased did in fact use real Cree emitters as advertised but they were under driven so much that the light output was no where near the potential it should have been. I've had the same experience with Osram and Epistar based products too. Even in lamps which seem to have adequate heat sinking with large fins, metal PCB's attached to the housings with ample thermal compounds, the LED's are driven at 1/2 to 1/4 their potential outputs. I'm not sure if they're doing this because of poor quality drivers unable to handle higher currents, poor PCB traces unable to handle higher currents, or just for sake of lower failure rate with what could be 2nd or 3rd quality emitters. I have noticed with Cree XM-L and XM-L2 based products color binning is poor, often two or more LED's will be of slightly different color, but equal intensity. At distance the color variations are mixed by the optics so it's not really a problem for something simple like a bicycle light or a cheap 'throw away' flash light. I just can't get over how under driven the LED's are! There has to be a reason, but I haven't figured it out yet for sure beyond my speculation of poor quality 2nd and 3rd rate parts, not every Cree or Osram emitter is going to run at full power with full lumens, much like not every Intel or AMD processor will run at the full speed the design is capable of. I'm not qualified to make the call on why they under drive so badly though, and we know the vendors on eBay don't know either. My Chinese is too poor to ask the factories directly so that's out, all I can do is speculate.
My rule of thumb for most Chinese LED products is expect 1/2 to 1/4 the advertised results. If it says 30W it's likely more like 10W, if it says 3000 lumen it's likely closer to 1200 lumen, based purely on my own experiences.