The short answer to your question is that if you want to know for sure what the shutter speeds are on your camera you will have to buy an inexpensive shutter tester that runs on Audacity.... or build one.... or shoot a test roll of film and see how the shots come out. There are lots of schematics on the internet for these testers, and as an engineer you would probably enjoy building one. They're very accurate, but limited to 1/1000. I've been using one for nearly 15 years.
Generally, if you read in an ad that "all the shutter speeds sound good", this is a good sign. It means that the seller is knowledgeable enough to know roughly what the speeds should sound like, and that none of them are sticking. If on the other hand you read "all the little knobs and levers seem to work", you are taking a chance buying that camera. Usually those sellers are pushing shirts w/ little alligators on them, golf clubs, or doll dresses when they're not selling cameras.
A shutter that is one stop off is usually considered within tolerances, even after a CLA. If you have a Barnack type camera, you will have to remove the body around the shutter to test the speeds. It's much simpler to just shoot a test roll. A shutter speed tester will not tell you if the shutter is capping (you will have to take the lens off and hold the camera up to a light and fire it to see that, and good luck w/ a Barnack), nor will it tell you if the shutter has pin holes in it.
While it's true that you will seldom if ever see a SLR that has a shutter that runs fast, you will sometimes see leaf shutters that do this on their slowest speeds, and it's not a good sign. If you're lucky, it just means that the lens needs to be unscrewed and the shutter blades cleaned w/ lighter fluid and a Q-tip (lots of Q-tips), but it could also mean that something is gummed up or broken in the slow speed escapement. In my experience w/ Rolleicords and Rolleiflex cameras, it means something is broken when the camera fires at the same speed on every speed, in which case you are better off selling it w/ an accurate description and buying another camera. A shutter CLA on these cameras is usually far more money than the camera is worth because the shutter is so hard to get to.
Like Roger, I once had a Leicaflex that had a slow shutter and it took perfectly exposed shots. Those negs were beautiful to look at on a light box. The odd thing is that the speeds were not slow in a linear manner. One may have been one stop slow, another may have been right on the money, and the next may have been 1 1/2 stops off. It didn't matter, it took perfectly exposed shots every time. Go figure.
