The bushing tool body wants to turn as you try to remove or install the bushing, or the bushing seems very tight

Most likely the thread of the driver bolt needs lube. A little grease or oil on the threads will make the tool much easier to use. Also make sure you have the small nylon washer under the bolt head. This allows the bolt to spin in the driver.

Usually the first indication is a slight clunk in the rear suspension. The other sign (and the easiest way to test it) is if you notice movement or a clunk when you pick up the rear of the bike by the seat.

To test this gently lift the rear of the bike using the back of the seat. If you can feel movement, use you other hand to hold the various pivot points starting with the first shock mount (ie where the shock joins the suspension linkage). The movement may come from other points but the most common is the shock bushing.

Shock eye bushings (aka DU bushings) are designed to allow the shock to pivot on the eye. The mounting hardware should remain tight within the frame. Over time this movement (and the stress of you pounding it down the track) causes the bushing coating to wear thin producing play at this joint. The bushing is the designed wear item and if replaced as required the mounting hardware should remain is good condition for a long time.