I believe the % your referring to is monthly rental income of purchase price/cost.  

One way is to increase the rental income on the building as well as think about other streams of income from the property, perhaps there's parking or storage you can rent to their neighbors who would need it?

Yes physical cash, I'm also worried about putting the money in to others bank accounts and then them getting taxed on the money because it'll look like income even if there just transferring the money to the lender.

The average annual gross rental income for a platinum one-bedroom condo is $36,000 and rents out an average of 170 nights per year. 

If I had given them a loan with payments, it affects the debt to income ratio.

The rentals are a nice way to acquire passive income but I want to turn real estate investing into my full time job.I have been looking into a bunch of areas such as Flips, Wholesaling, Pre-foreclosures etc. 

EXAMPLE:  These are fictional numbers, as I don't know your market.Shared Residence: $600 EACH room = $3000 GROSS POTENTIALSingle Family:  $2300 GROSS POTENTIAL RENTDuPlex:  $1500 PER UNIT = $3000 GROSS POTENTIAL 

Would you accept a tenant for a $2,150/month rent with the following situation:- They own 2 restaurants so it is hard to verify their actual income VS the company.

Trust me, I can make far more money with other forms of income, but this is pretty passive.  

For example, states like Texas have no income tax but higher property taxes, which can impact your strategy.