Should I still call a roofer or would someone else be better an diagnosing a ventilation issue?

If you are too far away to have driven there, this sounds like a problem which could have been diagnosed and solved on the spot via telephone. 

We had to show our house to potential buyers, with no middle man, no help in negotiating.It took 18 months because we are on a Humanitarian Reassignment: my husband's mother was  diagnosed with stage 4 cancer, and we PCSd to take care of her in her last months. 

He charges $75 to do the repair and even fixes the shelf in the next room.I have another vendor #4 who doesn't have a snake to do this kind of job, but he's usually around and can diagnose the problem and let me know what's really going on with it, as I am rather busy and often have to take the word of the tenant and photos etc to find out what is wrong.

it is harder to know exactly the cause with the third party manager involved.....for example, if you said you got calls and no showings, I might diagnose curb appeal issues. 

@Chris Mason Actually my daughter has been diagnosed with a learning disability but there's no physical disability.

Yesterday, I hired a different repair company and he diagnosed the problem as not the washer broken, but a loose wire in the wall outlet.

I was always told that if a mechanic started diagnosing your car based on what you tell him the symptoms are, you need to find a new mechanic.  

Do they diagnose and service or is everything a replacement?

A deal I recently did went like this.This seller was diagnosed with cancer and didn't want his wife to get stuck with the stress of landlording.