I've seen a number of comments in various threads about people getting stuck with 'bad' lenses that they end up having to send in to Canon for repairs, adjustments or replacement. Does Canon charge you if the lens needs an adjustment because it wasn't properly set up in the first place? Is there a quick and easy way to test the lens in the camera store to rule out most problems or will the clerk perform any tests at the time of purchase. I was thinking it might be beneficial for everybody if there was some kind of testing unit in the camera store that would test the lens's focusing, etc. I wouldn't even mind paying $5 to have the lens tested as opposed to having send into the manufacturer.
It is not possible to test a camera lens in the store for some of the more subtle issues like decentering or autofocus accuracy, and you can't use FoCal in a store either.
To have a lens tested, $200 or more would be a more accurate cost than $5. Its time consuming, and a store has to pay a good camera tech fairly well. Some tests require a lot of space, you can do it outdoors on a nice day, but the cost for a indoor facility would be high.
The percentage of new lenses with problems is very low, but they do happen. Test your lens as soon as possible, and you can exchange it for another at some stores, or Canon will repair it for you.
Buying a used lens is a different issue because you are dealing with the possibility of a lens that has been decentered by receiving a blow or by dropping it. The lens may look perfect, but have some internal damage.
I never buy a used lens unless I can return it, or unless the price is low enough to allow me to have a average repair done.