How do you know it needs replacement?

Took my 2005 in for an oil service at (63,000 kms) 40,000 miles. SA said thrust rod bushings need replacement 'soon'. How do you (they) know the bushings are bad? I don't thins the tech test-drove the vehicle outside of the dealership.

I don't mind changing them if they need changing... I just want to make sure I'm not falling victim to a money-grab.