Excellent. Missing: check that IS works on OIS lenses.

Thanks for sharing your input. I've added this caveat to my original post.

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Good point. I don't have any experience with OIS lenses. Any ideas on HOW one would validate this functionality?

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My understanding was that "no returns" means that if the buyer finds that the item is exactly as described, then there is no option to return it . Certainly if an item is not as described, there must be a chance to return it!

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The buyer will need to destroy it, submit proof and they'll get their money back. They get to keep the destroyed item. There was a story while back about a antique violin, declared a counterfeit and destroyed rather than returned.

Can anyone help in describing how one would validate that Image Stabilization is functional on OIS lenses?

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Lens element separation occurs when two cemented lens elements begin to separate.

To identify it, look through the lens at a bright light or brightly lit wall for any bubbles or patches of discoloration at the element edges. Separation can appear as an iridescent or rainbow-colored crescent on the edge of the lens element. Separation is difficult (read: expensive) to repair, so if you find evidence of it in a lens you are evaluating for purchase you should probably walk away.

A lens diagram can be used to determine which elements (if any) of a particular lens are glued. If a lens contains no glued elements, then element separation can obviously be ruled out.

Here are some samples of how lens separation might look (click to view full size):

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Oil or oily residue on aperture blades can hamper the action of the blades and lead to your photos being overexposed; dry blades work best. Oil will appear as a dark and/or shiny discoloration on the aperture blade. Oily aperture blades may appear as a six- or seven-petal flower pattern when the aperture is fully stopped down (i.e. closed).

If you suspect that oily blades may hamper performance, use your finger (or a toothpick) to slide the aperture control rod to stop down the aperture; when the rod is released the aperture should immediately snap shut.

This condition can be caused by when a lens is subjected to high heat (e.g. left in a hot car or near a hot light source) for an extended period. The heat can cause the lubricant in the focusing helicoid to break down and seep into the aperture mechanism.

Oily aperture blades seem to particularly inflict some FSU (Former Soviet Union) lenses (e.g. Jupiter, Helios, Industar) as well as some Kiron/Vivitar lenses from the 1970's.

Removing oil from aperture blades is not all that difficult, but it will require disassembling the lens nearly completely. An ultrasonic bath can be used to remove the oil from the blades. You can expect to pay at least US$50-100 (perhaps much more depending on the lens) for this service in a reputable repair shop, so take this expense into account when valuing the lens.

More info on oily aperture blades can be found in this post on the KEH blog.

Here are some examples of how oily aperture blades might look (click images to expand):

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Lens haze or cloudiness can have a number of causes. Haze is often caused by oil from focusing helicoid grease that vaporized and gotten deposited on the lens. Sometimes deteriorating lens coatings or failing cement between glued elements can also appear as haze.

To diagnose haze, hold the lens up in front of a dark background and shine a light through it from the front. Ideally you won't see a major change in what you see through the lens (which should be a dark round spot), but if haze is present it will appear as tiny spots or as general lightening of the opening caused by light reflecting off the hazy element. Do this same test looking through both the front and rear elements of the lens.

Haze may or may not have a noticeable impact on image quality depending on the lens design and/or where the haze occurs on/in the lens. The only way to determine the impact is to shoot some test shots with the lens and evaluating the contrast which the lens is capable of delivering. Look also for additional lens flare which might be caused by the cloudiness.

Since there is such a wide range of potential problems/solutions to this affliction, it is probably best to avoid any lenses you encounter that exhibits haziness that impacts IQ.

Here are some images of what lens haze might look like:

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I would also add to the aperture section especially, a part about the relative value vs cost, depending on user's handiness.

For example, aside from one touchy spot, where I would have been able to make it work fine even without getting it correct, I got a lens that regularly retailed at $100+ for $15. Able to clean up the aperture blades, and saved a ton of money. Would I have done it if the lens cost was $60 damaged, or only worth $30 fixed, or if I couldn't see it? No to all of the above. Sometimes though, there is the exception to the rule where a great potential value and some elbow grease may fix a lens that has minor problems.

Again, I would echo the above, do tons of research on the prospective lens and difficulty fixing the problem and make sure you aren't burning your effort away uselessly, or that the fix is beyond your level of expertise, or the lens overall isn't worth it. Just sometimes everything works out, and you get an amazing deal.