Do they gain somehow from me doing this?  

Some potential drawbacks to keep in mind are:Additional closing and loan origination costs (two transactions/mortgages instead of one) - speak to your lender and title company about costsTwo insurance policies instead of one - probably close to double the insurance cost as compared to a duplex - get a quote from a good insurance agent and compareTwo sets of property taxes instead of oneThese certainly aren't deal killers, and the benefits noted above may outweigh the disadvantages.

The cost far outweighs the benefits for that amount of money.

This longer life would negate some of the tax benefits that are afforded to owners of residential rental properties (due to the shorter depreciable life on those types of properties), and would most likely cause your rental income to be taxable more often then not, right?

It's not something I would be opposed to, I actually think there is a benefit to both the tenant and the landlord.  

But, since you don't yet know this tenant, if you want to give the benefit of the doubt, I would give them a letter that says: if they don't pay the September rent by Monday, you are evicting.  

You are gaining it. 

Real estate Agent/investor in Fort smith Arkansas & Mississippi here to gain knowledge and hope do business.

I concur, and have the benefit of living in this exciting market place!  

And having a license would benefit me in that case, cause if i sandwich, any transactions done represent myself and not the seller but I'm still protected if people get sue happy.