Moisture / water / mold, knob & tube wiring, foundation issues, ancient plumbing, rust on the breaker panels, termite tunnels, powder post beetle damage, cedar post supports, improper footings, temporary lally columns, etc.As to writing an offer, that's a sensible and common approach. 

Kevin,Most of our Insurance carriers have a problem with Aluminum wiring (similar to the way they feel about Knob & Tube). 

You can certainly piece together the articles, blogs, and videos from your local & national Self Storage Association, or through Inside Self Storage, or You-Tube (and soon Bitchute) Videos.Also, there are many, many articles in BIGGER POCKETS over the years giving good information.

Here’s the story on that...I knew when I purchased I would need a new roof in a few years, electric could be an issue because it is knob and tube, hot water heater could be a problem because it is 9 years old and the pipes going to out to the street are cast iron so if they burst I would be screwed.  

Also, porn. 

spend the extra 10 or 15 bucks on a good caulk gun there's been so many times I've ruined a tube of caulk or ruined the gun itself and it is just so much nicer to have a good caulk gun you'd be surprised.

Looking in the Cleveland area and I'm noticing a lot of knob and tube wiring.

I'm in the process of closing on a property in NC, and the visual inspection has turned up evidence of termite damage and previous treatment:"Termite tubes in between rear left garage slab wall and drywall bottom.

I was looking at the multifamily properties in the area quite a bit, however they all seemed to be built in the early 1900's and had knob and tube wiring and cast iron pipes...cash flow is really good on them but the potential repair costs drove me toward small slightly newer Single Families for now. 

If the agent doesn't have time or patience to show you how he/she reached the conclusion then get someone else who can show you step by step whatever you need to know .You can ask them before you use them if they're ok with a beginner like you who needs some explaining along the way .I also recommend reading books, listening ,to podcasts, watching you tube video's and of course bP forums .Don't forget the BP tools ,estimator for rent ,rehab etc. it makes things much easier.