Was your original request just to sweep the chimney and this turned up? What's that saying about giving a kid a hammer and everything is seen a nail? Might be the same thing with these cameras. Have you ever had a chimney fire? Do you use your fireplace much? Stainless steel liners are expensive but they are necessary in certain situations.

No, jrb451, never had a fire. We use it two or maybe three times a week during the coldest part of winter, and never had a problem. This was a routine cleaning and inspection, which led to getting a second opinion, and then a third.

I'd think the likelihood that a 78 year old flue DOESN'T have damage is zero. What would you expect the condition to be after so long and with what might have been shoddy construction practices common to that era?

Two have looked at it and said there's problems, one didn't look at it and said it's fine. So far there's one foolish person involved, don't make it two (ie, you making the wrong decision).

If you use it so frequently, insuring it can work correctly and safely doesn't seem unreasonable.

A properly maintained chimney with terra cotta tile lining can be in fine shape after 150 years or more. It's simply not true that damage is inevitable after 78 years. It's also not true that modern construction techniques are automatically superior to those used when your house was built.

What to do about your chimney is another question. Serious cracking of terra cotta tiles is almost always the result of a chimney fire or, possibly, movement of the earth.
If the cracks are severe enough so that the lining is no longer capable of doing what it's supposed to do - providing the first line of protection in case of a chimney fire, providing a relatively smooth surface to enhance the draft and make cleaning easier - then relining is probably necessary. If the cracks and pits are superficial - pretty much effecting the surface glazing only - they may have been there when the tile was installed and present no hazard. See if your local fire department offers free chimney inspections. Many do. This would be a good neutral fourth opinion. I am inclined to believe the third opinion that relining is not necessary. Lining isn't exactly a scam and certainly would not do any harm, but selling and installing liners is far more profitable than just cleaning so the incentive to exaggerate the need is always present.

I had two chimney experts with video cameras tell me that my 78-year old terra-cotta chimney flue, serving a single wood-burning fireplace, is cracked, chipped, and dangerous.

They are 'telling' you as opposed to showing you? As in seeing the camera images live and recording the inspection on a DVD? (I would insist on seeing live images and not just a recording (of what might not be your chimney). Once you're convinced that you have a recording of your chimney, you can seek second opinions.

Thanks, everyone. I saw the cracks at the mortar lines on the video screen but as guy # 3 pointed out, it's impossible to tell if those cracks go all the way through and allow any smoke or gases to escape the flue. On the other hand, whenever I sell this house, an inspector might well poke a camera up there and lead nervous buyers to conclude that they're looking at a dangerous defect. So I'm thinking I'll bite the bullet and settle the question now rather than later. As for mid 1930s construction techniques, they built great walls and were masters with plaster. But their electricians were, by today's standards, cowboys and practical jokers.

In general, yes, chimney relining is a scam.

In your particular situation with a fireplace flue lined with tile liners in pretty good shape (a crack or chip here or there) it's definitely a scam.