I like to be safe, so I would hire the plumber. In my experience, and especially now days, you should be able to find a reasonably priced plumber. Once you get it done professionally, you will never worry about it again. Isn't that worth the money?
They told me that terra cotta lines were rarely used after 1973. Terra Cotta have the highest risk of needing replacement. Also the number of trees in your front yard are a component of risk, and a steep yard will increase the potential cost of sewer line replacement.
For information on other hazards, such as maps of undermined areas...see my website or contact me.
If they are doing the sewage lateral line inspection, they would be using a camera to look into the lines...that should be sufficient. If you want, you could ask to be present for the inspection or review the tape at the municipal building afterwards.