Canon Kit Lens 18-135mm IS 3.5-5.6 IS - Why such a wide price variant?

[theantiquetiger]

I was thinking about selling this kit lens that came with my 60D, so I looked it up on eBay to see what they are selling for. They sell (not just asking price) for anywhere between $200-$600.

Am I missing something or are people that dumb when shopping? I was told it was about a $300 lens when I bought the camera.

***Edit***

OK, I went back and looked, one is an IS and the other one is an IS STM (the higher priced one). What is STM? Mine is the non-STM model.

[Iguanasan]

From: Canon EF lens mount - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Canon_EF_lens_mount)

Stepping motor

Canon EF 40mm f/2.8 STM pancake lens
Stepping motor (STM) lenses were first announced in June 2012, alongside the announcement of the EOS 650D/Rebel T4i/Kiss X6i. Two EF-S lenses and one EF lens featuring this technology are now available: the Canon EF-S 18-55mm f/3.5-5.6 IS STM and the EF-S 18–135mm f/3.5-5.6 IS STM superzoom, and the Canon EF 40mm f/2.8 STM pancake lens. A fourth lens with this technology, the EF-S 55–250mm f/4-5.6 IS STM, has been announced and is expected to be available in September 2013.
Canon claims that this technology allows smooth and silent autofocus, and with compatible bodies (the first of which is the 650D), will provide continuous autofocus in live view and video.[9] Unlike USM, STM lenses use focus-by-wire to enable full time manual mode, which means that rather than manually moving lens elements, rotating the focus ring commands the stepping motor to change focus. This means an STM lens's focus cannot be retracted by turning the focus ring while the camera is off.
Both lenses introduced with the EOS M, the EF-M 22mm pancake prime and EF-M 18–55mm zoom, also feature STM technology.[1] The most recent EF-M lens, the 11–22mm, is also an STM lens.
All stepping-motor lenses are marked with the letters "STM" on the front of the lens as part of the model designation.