It's fine, just check the feedback and description - if anything is unclear ask the seller to confirm.
I've sold a couple of lenses on ebay in the past and one guy actually returned a lens because "there was a hair inside it".
In my description I clearly stated it was an old lens in full working order and in excellent condition, but it may have dust etc inside that doesn't affect the image quality.
I accepted the return reluctantly and the git kept the lens hood. I checked the lens over and couldn't find a single hair inside the lens. Sold it on here after that and the buyer couldn't see the hair either.
So on behalf of sellers everywhere, be realistic - don't expect the lens to be dust free - I doubt you could find a single lens anywhere without some dust inside the lens.
I'd rather buy on the classifieds than on ebay, simply because the prices are better and you're more likely to get something that's been looked after!
But please, if you're going to buy on ebay don't screw the seller because you didn't read the description or have unrealistic expectations. Yes I'm still bitter about it, cost me £5 to post it, another £5 to reimburse the seller for return postage, lost the hood to the thieving ******* and I'm sure I still had to pay fees on top of that. Considering it was a cheap lens in the first place and I was selling it as I needed the money to cover the upgrade cost to a slightly faster lens I was truly shafted by that guy.