TxBuilder, I'm glad that you found your problem, but, its not always roots.
Some times it can be clogged up pipes, like grease in the laterals, or detergents with phospates used to be a bad one, they hardened like concrete. Also, I may have been a plugged up vent, or even a collapsed sewer line.
As a Waste Water Plant Operatore for 26 years, recently retired, I used to go out with out "line gang" and we encountered all kinds of problems, in the sewer system and laterals from homes. If your lateral was laid level, then there was a whole host of problems (yes, we encountered a few of them). Weeping Willows were the worst offenders of tree roots, we banned thier growing in our town because of that!
Also, if you rent a "snake" and you lose the "cutter" in the line because of a collapsed sewer line, then you not only have to get it out, but pay for it, if you dont return it promptly, which isnt a great thing to do... But, like you, I advise people to rent thier own snakes also, as I never call a plumber
Just my two cents...