I told them they are responsible for blockages. 

They will be back today since this is a bigger job and they might have to open pipes at sink etc. to find blockage.  

He also suggested to me that very regular furnace filter changes will reduce blockages and so improve air flow to the house.

As others mentioned if it has galvanized pipes they can be deteriorated and causing blockages.

@Jon Holdman yes, I think the rodding and roto-rooting is the same thing.I found this article helpful to understand all the blockage issue in sewer:http://www.raviniaplumbing.com/blog/everything-you...Also this PDF from U of KY also have some in depth info - if you want to digg deeper in your research!!

Also, if it's a multi, and the blockage is in the main sewer line, you have no proof it's him. 

But for whatever reason i have this mental blockage in my head that “I am taking advantage of the poor people by purchasing their property pennies on dollar,  I just feel it’s not right”.Can somebody please help me getting over this mental blockage ?

I had only one plumbing problem over the years resulting from the blockage of the overflow pipe in the tub causing an overflow.

Depending on age, it could be clay, which is particularly susceptible to breaking / blockage.

How would that fix a blockage, and how much might that cost?