Plumber says we must replace line
Our cast iron pipes are below slab. Plumber's Camera inspection shows two 3-foot bellys in the line, right under the center of the house. To dig up and replace would be major work, drywall, carpet, and kitchen. The laundry, kitchen and one bath all feed into this line before drains into the main line to the sewer. Washer backs up every time now as it drains. Dishwasher too. Toilet bubbles regularly, fills, then eventually drains. This problem has been going on for a long time. Water lines appear clear, this is a sewer line issue. House is 45 years old. What questions do I ask the plumber? How do I know who to trust.