Common problems are pipe leak, even separated PVC on a drain (since you say under the sink), rotted window sills, dirt up over the foundation allowing water in between the brick and the foundation, or a dozen other things.

The house most likely has major mechanical issues (foundation, termites, etc).

If the roof, foundation and major mechanicals are in good shape, you shouldn't be facing large cap ex anytime soon.  

That is is an excellent way to long term wealth, and it sounds like you've already laid a nice foundation financially.If so, there are a few books I could recommend, although I focus primarily on flips, with some other types of deals worked in.  

If the current owner has proof of rental payments, I wouldn't worry about collecting rent.4) Ask about roof/furnace/foundation/plumbing and electrical repairs.

We actually existed our retail property division in April to a national vendor, this department would take on any homeowner but not any property we were selective, but we were constantly battling massive overhead cost due to the unique qualities and building found at every site, being scattered site with over 700+ doors under management was super complex and required a lot of staff.

My foundation to this interest was ingrained by Rich Dad Poor Dad and Rich Dad's advisers. 

We have done all the work ourselves minus some foundation and heating/cooling work.  

We are interested in any properties that have a profit margin, whether distressed, mold, foreclosure, or foundation problems.

I had one HVAC company charging me 3x the Home Depot price of a heater, so I got a good contractor (had him some 15ys now) to do the job for 2x - - nice savings.Had an issue with a well know plumbing company wanting 14k to tear out a bathtub and jackhammer the foundation to solve a backup problem :ouch:  I put the job out to bid and we resolved the issue thru the exterior wall - - 2.5k.