Watch out for certain questions being asked by the worker, e.g. “Is your husband home?” or “How much do you know about your drainage system?” Some companies use questions like these to feel out their targets and take advantage of them.
Some dishonest companies send employees out in pairs. While one distracts the homeowner with questions or conversation, the other “inspects” the premises for supposed damage. It is not uncommon for them to plant “evidence” of a broken sewer line, scaring the customer into paying for unnecessary repairs.
Nowadays, companies use video cameras to inspect inside drains. But make sure you are not being played for a fool (literally). Look at the video carefully to see if it is a “rerun” from a previous job.
Do not allow a company to convince you to use a liner for your pipes. They are not practical. They decrease the diameter of the pipe; they take the shape of the pipe itself, so if the pipe is crushed or contorted in any way, the liner will be also; and they are just as expensive to install as cleaning out the pipe.
And of course, you always want to do your research to verify the company you are using has a good reputation within the community, and is in good standing with the Better Business Bureau.