Tenant said he loved living here!

[Jeffrey K.]

So... spoiler alert...this is a bit of a humble brag but I could use some advice too! 

The 1st day I bought my fourplex I overheard a conversation, through an open window, where the tenant in unit #2 was saying that he "hated living here." Currently, I have a yard full of dead weeds, a dirt pile in the parking lot and a litany of other half started projects around the complex. Despite all that, the tenant in unit #2 renewed his lease and told me he loves living here in spite of me raising rent and imposing additional rules. I believe this is a reflection of my leniency and ability to work with him. I loved hearing this, and it was an affirmation that I was doing something right. 

However, this leniency has also gotten me in trouble...aka unit #4. This guy moved his sister in and I allowed her to live there for a few weeks to get a foothold while moving to a new state. But, while doing some repairs in his unit I found out the sister moved her kids and 2 dogs in as well. So now there are 5 ppl and 3 dogs in a 2 bedroom apartment. Although I have gotten some reparations and they are moving out next month, I fully realize that is was the same sympathy and rationalization that I used with unit #2 that got me into this mess. Where do you draw the line? what are the hard and fast rules u use to insulate yourself against ppl taking advantage?