I had another guy come scope it for a second opinion and he said he jetted it, got through any major blockage and it should be fine.

There also could be blockage in your sewer line.  

Our plumber does give us a description of the blockage or issue and we screen this for tenant responsibility- ie superman was snaked out of the toilet, cat litter was dumped out of the now unusable garbage disposal (also interesting in non pet friendly properties) and we will pass that charge on to the tenant with appropriate explanation. 

I have a house that had problems with unruly roots which caused some plumbing blockages.

If it has galvanized metal pipes, those eventually decay and start to flake, which causes blockage.

Additionally, some contractors will also install an ejector pump to pump waste from the property over and above the check valves back into the sewer line as once the check valve is activated, the waste from the property is unable to leave and go into the main sewer line until the blockage is resolved.Although, I can't personally recommend one specific contractor, I've read good things about The Real Seal, although they may only work on another drainage options (i.e. drain tile). 

If it’s on a slab, duct scopes can reveal blockage, disconnects, decay, and is a great idea.Scoping a sewer line is a great idea if there are a lot of trees on the property, people drive or park where the line runs, or the house is very old.

A blockage in the city sewer main flooded our dupex's lower unit with two feet of sewage.

He found that the cast iron under the basement has some corrosion and would probably need to be replaced as another blockage would probably happen.

The head pressure of the water will usually push through whatever blockage is in the trap arm between the sink and vertical stack.