There are a few options.
1) You got yourself a fantastic deal. If the laser comes with a robust diode and comes from the factory at 50mW of 532nm radiation, that's great.
2) You got a pre-modded laser. It could be a Leadlight 105 modded to 50mW. Not bad, but you could have gotten an unmodded one and done it yourself to save some money (and gain some experience!).
3) You got a laser that emits IR as well as 532nm. If you have access to an IR filter, shine the laser on your hand for a moment without the filter, and then with the filter. If the laser seems weaker with the filter, it's emitting an invisible wavelength that makes your laser appear weaker than it is (which is dangerous).
4) You got totally ripped off. The 50mW claim could be a flat-out lie. That sometimes happens on eBay.
I would think that 2) and 3) are the most likely. If you have a 5mW 532nm to compare your new laser to, that would be useful. You could also send it to Craig at The LED Museum to test it if you wanted to...
AND WELCOME TO CPF!!!
