I recently sold my Canon 30D on eBay... I now have a buyer saying there is a smudge, not dust, but a smudge in the corner of the sensor. Now I have only ever blown air into the camera with a giottos rocket blower... it wasn't even used that much recently and when I last used it properly the photos were crystal clear. Further to that I thoroughly cleaned the body of the camera and checked the sensor for dust before I sent it off. This person is now telling me that upon receiving the camera they took some test photos and noticed a big smudge in the corner... I'm pretty bloody sure I'd have noticed it too...! I'm not sure that they knew not to touch the sensor, as from their emails I get the impression they might not know the workings of an slr camera too well... so I'm reckoning they must have poked at the sensor or something? Maybe an oily fingertip? Regardless, they are suggesting sending the camera for professional cleaning and in good faith I have offered to pay half... however I'm a bit concerned that if they have done some serious damage they'll be billing me for half a new sensor charge, which I sure as hell ain't paying. I've never had to send a body off for cleaning of any sort and only ever had a dust problem on a previous camera which I removed with air being too chicken to physically clean the sensor... I'm convinced this camera was spotless!! Just wondering is it likely to be serious damage? A smudge to me sounds more like a substance on the sensor as opposed to an actual abrasion, and I know dSLRs have a clear glass coating over the actual sensor. In this sense I'm hoping its just something that can be cleaned off rather than needing replacing... Tell me what I want to hear people... please?