If you have an older house, getting the someone to do a video sewer scope inspection can possibly save you thousands. The issue that I run into on a home inspection is that I do a visual non-invasive inspection (mostly) and the sewer line is buried under ground making it outside the scope of what I do.
Based on the age of the home, I can make some educated guesses on what material - ABS, cast iron, concrete, Orangeburg - you may have connecting your home to the city sewer or to the septic tank. What I have no way of telling you is what condition those pipes may be in.
When I have some concerns, I recommend you to a professional who has the equipment - a sewer scope which is a camera on a long flexible lead that gets pushed down the sewer line, sending back images to a video recording system.
Ideally, this operator will send the probe to the connection with the main sewer line or septic tank and report back what the material is and that it is in good condition. Unfortunately, as plumbing pipes reach the end of life period - and this is occurring more often with the post-WWII homes approaching 70 years old - we're seeing more failures.
The failures tend to aggregate into two categories. The first, material related, is simple degradation of the pipe. Orangeburg pipe - basically a toilet paper roll impregnated with tar - simply falls apart. Cast iron has rust issues.
The second category deals with time and the effects on the conditions around the pipe. One example is a failure of compaction in the soil that causes the pipe to shift or even break. This can be a problem with modern drainage piping - the lines often will develop sags that restrict flow. Another one, a particular problem in older neighborhoods are the wonderful mature trees.
I had a beautiful jacaranda tree in my front yard when I lived in Southern California. One of the reasons it was so spectacular was that it had a steady source of nutrients - my sewer. Trees are opportunistic and this one found all the joints in the clay piping and invaded at the seams where each hub piece was joined.
I bought that house before video sewer scope technology matured so I didn't get the advanced warming - the total tab was nearly $5,000 in repairs. Now that the technology is here, I recommend it to clients with older homes.
The actual wording that I use is " It is not unusual for older homes to begin to have problems with the waste drainage system. These systems are not readily visible but can be imaged using a video sewer scope system. Recommend having a video camera line inspection for potential blockages in the main sewer line."
It's up tot he client to make the call obviously - but it awfully cheap peace of mind.