Does anyone know why a plumber who still need to come out when he seems to have fixed the problem?

its possible he only had a small snake with him. that exact thing happened to me last year. I had my 50' footer and I never hit anything until about 49 feet. when I pulled it out, it had tree roots on it and the homeowner was happy I had unclogged his line. 2 days later, he called again, (just as I had suspected) and I had to go back with the hundred footer to remove the remaining tree roots. so, you can try it like it is, but I always prefer to run my snakes all the way to where the meet the main sewer line. I like to give a 1 year warranty on my work, but if the owner insists. 95% of these kinds of calls, I can get away with my 50' because its normally a clog close to the house, hence why I only brought the 50' the first day. good luck!! $150 an hour is outrageous tho. I charge 75 an hour, and I always do them in less than an hour. if he has a snake, theres no need for jetting. I stick a garden hose in behind mine to wash the clog on thru and keep my snakes clean, but.......o-well.

Just refuse and hire someone else if you have issues in the future.

But if you had roots in the pipes, you should be budgeting for a new one which will cost you about 8-10k in dollars if you're in most parts of the USA.

Roto Rooter sells these chemicals that will poison roots, and you can just be regular about using it. If the food isn't tasty, the roots will go away, usually.

fyi - this type of repair takes many hours, always, it's not just him wasting your time, focus on getting the insurance money and the insurance company to get someone out to you asap to clean up for "free" (not really free since you've been paying them insurance fees). That toxic sludge can cause black mold and then you'll be really sick.

What i'd like to ask is: What's to stop more roots coming into the pipe ?

I was warned that a dangerous tree was growing close to a main sewer near my house, so I paid someone to cut the tree down and poison the stump. What's in a sewer ? Water and sh*t. What more could a tree want ? Ask yourself what you can do to stop the roots growing back again.

Very often we can get things working but it isn't 100% like we would like. Usually do to parts or tools we have on hand at the time. So we follow up with the right stuff to do the job properly. If you don't trust the guy, then tell him not to bother, just don't hold him responsible.

More than likely he is wanting to complete the job so you will not need to call him back in a few months when it stops flowing again. You should have insisted that he explain what he is doing and why he needs to come back. He is working for you not the other way around. When he comes back insist he explain himself. If he will not then fire him.

he said he didn't finish

he could have cleared part of the pipe which is filling up with water but slowly seeping through giving you the illusion that its cleared when there is still blockage further down the pipe to be removed