A drain snake "may" work if it is a clog in one of the smaller diameter pipes. If it is in the main drain, he will need to rent an auger with larger cable and cutting heads. If it is tree roots, this will solve the problem for a while, but will need to be done again later. I did this yearly for a friend of mine. One thing you must remember about tree roots is that they have entered the line and this is weakening the structural strength of the line.
if you have never made a mistake, you probably haven't done much.