At the risk of being blunt, I believe that some of the issues could have been prevented with better foresight and/or screening, both for tenants and contractors.

A real estate broker shouldn't prevent you from doing so, but I'm not 100% sure of that, I suppose it would depend on the broker.

In that case, how can I prevent the tenant from bringing an unwanted person to the home ? 

which are the best option to prevent evictions ?. 

I've sat in on a few webinars lately and I'm really interested in implementing this as one of my strategies.

As stated, I've not yet implemented this strategy, so please chime in @Mike R. or others that may have more experience in this strategy.I've successfully deployed combinations of the 1st 3 above and have a portfolio of cash flowing properties in SoCal.

How do we handle this and prevent it from happening in the future?

The list from the county allows me to filter mailing addresses, but there are a heck of a lot of other information I don't understand - mainly with respect to the current status of the delinquent owner.I spoke to the county tax office, but they advised that their policy prevents them from discussing the identifiers.I guess I'll have to take my own advice, and keep asking until I get a result!

It's tough to implement though since I still find myself reinvesting into the business since there is always another great deal and once you get into it, it's tough to pass up.

My theory is whatever my business model is and whatever policy I have written down is what I go by and implement, I am not allowed to use my judgement to only my companies policies and practices