Record a video as I enter the rental, documenting it exactly how I found it.2.

But I also don't want the responsibility of paying for monthly monitoring/wifi, etc or tenants wanting to look at video, etc. 

Then we can post that video here to prove how stupid you really are. 

That cuts down on the chances of cracks spontaneously appearing in the stack and branch drains, or in the shower trap, which is very much one of the usual culprits in this sort of situation.The chances that three plumbers were "unable to smell even a slight odor" when they went and yet there is a powerful stench at other times is quite possible.

I just watched their video on Wholesaling and have been offered to buy the course, so I'm wanting to see some feedback from others who have joined. 

He was calling to report that he has repeatedly found his roommate watching adult videos on the TV in their shared living room, and more recently walked in on him in a similar state in their shared kitchen.I'm unsure of how to approach this one.

You can also watch this video that's pretty good motivation. https://youtu.be/jnARMZPHI58

A video of the entire house would also help.

I haven't done one but have a little bit of knowledge from readings and past videos that have crossed my path.

Reading all the books and watching the Bigger Pockets videos, everything seemed to make sense on paper but was so difficult in practice.