Lumens specs when buying a flashlight/torch. Why maglite has only 680lm but cheap ones have 900,000?
Well in your eBay-Link they are providing enough material to debunk themselves. They say they use a Cree XM L2 LED. So let's just look up what that thing can output.

Datasheet XM L2 LED and we see: even if it is driven with 2000 mA - which is quite the stress on the battery - it outputs 600 lm.

And they kindly provided a picture showing that they only use one LED and not multiple.

So they are lying or they measures the first production batch in unison and forgot to say they used 400 of these things.

Generally, you can expect around 100 lm / W and a handheld device is probably using 10 W maximum (okay might be 20 W or so with a good battery), so anything beyond 2000 lm is just unrealistic. 

If they tell you the 4000 mAh battery will last 6 hours, you can calculate the wattage:

4000 mAh / 1000mAh/Ah * 3.7 V / 6 h = 2.5 W. 

So 250 lm would be a realistic guess for the brightness. And yes, the 4000 mAh are faked as well - currently 18650 LiIon are around 3200 mAh maximum.



Okay, so how does the "brightest torch" from wicked lasers hold up with these estimates?

They claim 4100 lm using a 100 W OSRAM halogen bulb. The datasheet of that bulb tells us it emits 2800 lm. (Edit: the reflector does not affect the luminous flux, sorry about my mistake I often mix up the luminous units) I'm not really sure how they arrive at the 4100 lm figure - with 100 W it would be 41 lm / W, which is unrealistic high for a halogen bulb. So probably a bit of overadvertisement to stay with the claims of the cheap competition.

What about the power of this thing? They claim 100 W which sounds ridiculous. But they use 4 18650 batteries in series and give a low estimate of 20 minutes lifetime. Sadly the capacity is not given, but this is a really high current application, so the capacity will be a bit smaller - I guess 2500 mAh for a high quality cell.

4 * 2.5 Ah * 3,7 V / 20min = 111 W

So the math actually checks out and I think that it does what they say.