Worn Suspension Diagnosis

Visually inspect everything first and if you see something wrong, order the part then replace it. If you cant see anything wrong, go ahead and order the part they replaced last time and start taking it apart, and if that part wasnt needed, you could try and return it. If its the bushing like you say wore through, go ahead and replace them both if that was the problem. Other than that, its good to be tight with your mechanic.