In my last trip to the shop, the mechanics told me that I should replace my shock absorbers. When I inquired as to why, I don't feel that they were very clear with their answer, like they normally are.
So my question is, what are the symptoms that I need to be on the look out for to know when to replace my shock absorbers? Are there any tests that I can do?
FYI - My car just recently passed 74K miles if that helps anything.
It sounds like the mechanic is citing the maintenance schedule rather than a particular symptom. 74K miles is a good long way for a set of shocks and, while it's great that you aren't currently worried about their state, the vehicle will begin to suffer as they eventually fail. Here's a previous question that describes some of the rebounding that will occur after bumps. Before I replaced the struts in my wife's car, it was very annoying to drive around on and off-ramps: you would turn the wheel, hold a steady speed but the car's suspension would keep bouncing and never really settle down.
In my answer to that question, I listed a few things that you can easily check:
Insufficient damping (the bouncing continues and the suspension feels mushy).
Noisy motion (scraping sound when going over a larger bounce at slow speeds).
The Bounce test is a reliable way to go.
Were they flagged as needing attention at last MOT, certificate, or WOF inspection ( depending on where you are from ) I've usually found vehicle inspectors pretty helpful. However beware of Garages that want to show you oil leaking from shocks when you've got the car in for service. Happened to me once luckily I declined to have them replaced. Went for warrant of fitness inspection the next week. Flew through. It was another couple of years before I had to replace them
Shock absorbers almost always gradually wear, as opposed to failing completely. The bounce test mentioned is a good one, but most of the time, factory shocks are rated to about 60k miles. At that point they are pretty worn, but you can stretch them to 80k if you don't mind the ride.
If you want the best handling, you'll notice that all the aftermarket dampers have rebuild schedules between 15k and 30k miles. That's a normal wear interval for a performance rebuildable shock. OEM's will last longer, but they will degrade in performance starting around 30k miles and slow fall off from there.