A plumber came to our house yesterday because our main floor and upstairs (we have three floors and the basement toilet and tub were operating properly) toilets and tubs were backed up. He decided to remove the upstairs toilet after he pumped out the water from the tub that was left standing. He then augered the toilet and said "ok, I think I got it, let's turn on the water in the tub here just to be sure". After the water in the tub had been running for about a minute or two, he said "let me go check the main floor toilet to make sure that water is not running over" . He went downstairs and found that our entire dining room and hallway were flooded with brown water. The hard wood floor are ruined and so is our oriental rug and the grout in that bathroom is stained.

My question is if it is his fault for running the water in the tub that we had the flood? Shouldn't he have thought to have someone stand at the main floor toilet to make sure it was not overflowing when he turned the water on... in case he didn't actually remove the clog? It was a very large amount of water and I can't imagine it could have just come from that toilet...

(also, we never found out what was clogging the pipe, so he didn't know for sure that he had gotten it out).

Thanks for your help!

Anyone that works in your home should carry general liability insurance. Before you call a technician simply request a certificate of insurance. The technician's office will simply ask you for your name, address, and phone number. The insuring company will send you a certificate of insurance free. Then if you have a problem and the tech will not resolve it you have a means of recovery.
You are asking us to tell you the plumber made a recoverable error. This is something a judge will probably decide. Get your photo evidence and documentation in order and let the judge determine this.

Like Doug says this will be for someone else to decide, likely his insurance carrier. It was certainly an error in judgement since he knew enough to check the downstairs, just not soon enough. I am a bit surprised that two minutes of tub water could produce so much damage. The grout can be cleaned quite easily and the rug can be shampooed. The hardwood is a different story and I would accept nothing short of replacement including the underlayment. Sewage and wood do not clean up too well. You might start checking with your homeowners insurance carrier to see if backups are covered.