Hi (new member here),
Personally, my skepticism comes from the fact that the person is selling this 'haunted idol' on ebay. If I had an experience such as the seller has described, I wouldn't even consider putting the item up for auction to make money from it. I'd be either more curious to find out why it was happening, or I would get rid of it - take it to some remote place and bury it - if it frightened me or I felt it was in any way harmful.
Totally agree as well about the negative energy attached to it, if the seller is on the up-and-up. I'd steer clear of it.