We have enough passive income to live on and would supplement with house flips, etc.

Most get only $750/month so if they don't have additional family support, they often supplement their income by renting to couch surfers, selling drugs, selling plasma, and when possible, doing odd jobs for cash.

We really had to live off the CARDS until I got a great job and he finally took another part time job to supplement.

I do not supplement tenants rents and usually prefer to choose my own tenants.

Or are you looking to supplement your income with no desire to fo "full time" in REI.  

Hence I am already getting a great return and don't need to supplement with rent increases and late fees both of which are potential sources of landlord tenant friction.

Many of us have clients all over the U.S. and we supplement meetings with Skype or other video software. 

Moreover, if you want a supplant/supplement and or redirect your retirement strategies then you will have tertiary approach.

After one night and I got an email from the tenant saying she is severely allergic to cats and the smell of urine is all over the house.How should I handle this situation?

It's your money you are using to supplement their rent every month to the amount of $200 so you simply decide for how long and how much you want to pay them to stay there.If you raise it now by $100 then for the next year you are only paying them $1200 to stay in your property.