I'd stay away from ebay unless they were a known company as bluuray mentioned.
I've had absolutely incessant bad luck with them.
i'd add to the list above meredith-instrument / milasers.com / meridith-instruments, and aixiz. I think they do deal on ebay, and they are rather reputable.
But one-off sellers, steer clear. I think I'm at about 10 "dead soldiers" as far as ebay deals gone bad goes. I've got at least 6 dead ArIons, 4 dead HeNes, and 2 dead DPSS lasers due to my chances taken.
Just fair warning. Ask the seller if the laser WORKS, ask for a picture OF IT WORKING, and never EVER buy a laser described as "As-Is". The words "As-Is", simply translate to "broken", EVERY time, when it comes to ebay laser sellers.
EDIT: Ok, you responded while I was posting, sorry. I've gotten some of the cheap pens successfully from "motel263", while your mileage may vary, I've received every newwish-style pen $5-$15 I've ordered from him. And they've all worked, to a varying degree of power. (all above 5mW.) Some needed some DeOxit on the threads and battery spring to not flicker, but, I can live with that.