The key is to educate yourself on these issues, understand how to spot them, understand why some of these issues might (or might not) need to be remediated, and understand how they can be remediated--and the costs associated with remediation.The only issue that is a total deal-breaker for me, personally, is major structural issues (e.g.; major settling, serious foundation problems)...but even then, there are investors who specialize in buying and fixing those types of properties --again, the key is educating yourself so you know what you're getting into. ...it sounds as if maybe you're looking for a hard-and-fast rule like "DON'T buy a property with X", or "DO buy a property with Y"  --the reality is, REI is rarely, if ever, that cut-and-dry--it has many shades of grey, and it requires flexibility and creative thinking.Good luck!

@Martin Guerrero although you can (and often should) bring a GC with you (esp. if you plan to do a rehab), if you want to become a successful RE investor, you should make it a goal to become proficient at evaluating properties (meaning: evaluating problems with the property, likely costs to remediate problems, potential value add opportunities & associated costs, etc.).Ultimately, you want to become almost as good (or maybe even better) at evaluating properties as a GC and inspector.   ...Once you get to that level, you become an invaluable piece of your due diligence process, and your due diligence process involves three experienced pros (you, your GC, AND your inspector--which is much better than just a GC and inspector).  ...at that point, your due diligence process is multi-faceted and very robust (which is critical to success in RE investing)....you can make your due diligence process even more robust by adding an agent who is highly experienced in property rehabs, RE investing, and who understands how to evaluate properties.Good luck out there!

Should the HOA be responsible for noise proofing the ceiling if that would remedy the issue?

In California, the law requires that a licensed HAZMAT contractor quote and do the remediation which you can deduct from your purchase price.

But, the flipside is, she is also quick to remedy (while being apologetic) any HOA violations like leaving a bike in the common area, etc. 

Then we'll need to get with the correct provider of services (handyman, plumber, etc) and get that remedied ASAP.  

Depending upon what it is from, I would make a recommendation for them to remediate it.

My remedy I've thought of so far is to say we need to add them to the lease or they would need to vacate the property, if they'd like to stay it's an extra $100 a month if they're willing to pay it providing their background check comes back ok and we would need to further prove income?

That way, if anything goes sideways, the cash is there to remedy any property issues.Hope this helps!

Plumbing is something to check out, most MF properties that old are going to have some backups in the sewer lines that will need remedying or replacement, so get some quotes and consider budgeting for that.