We replace shocks and struts on all vehicles. There are several ways that these components fail. Some of the signs for YOU to look for are: excessive bouncing after hitting bumps. Another problem is harsh or stiffness in the suspension when hitting the same bumps. Does your car or truck feel like a lumber wagon compared to vehicles you ride in?
One of the most frequent problems is tire cupping or chopped tires. This happens when the suspension is worn and can no longer do its job and the tires start absorbing the shock. It causes tires to become oblong then back to round every time they hit a bump. Over time the tires will develop abnormalities on the tread (cupping/chopped) uneven wear. That uneven wear pattern will never come back out of the tire. We have seen many new tires ruined from worn suspension. DO NOT buy new tires until the suspension is repaired. Those old struts/shocks WILL wreck those new tires just as fast or faster than they wrecked the old tires.
Some other visual aids when struts/shocks fail: they leak oil, they become very rusted, they actually let the vehicle sag enough to weaken and break the coil spring, Trucks and SUV's tend to wear suspensions more.