Those are the owners that professional landlords prefer to take advantage of purchasing at a low number, value of income property being determined by NOI, and then bringing the rent to market rate.If you are a hobby landlord, which it sounds like you are,  then supplement their rent at whatever level you feel comfortable with.

I haven't taken it off of Airbnb yet and don't have plans to but I do plan to speak with a lawyer and draw up a separate supplemental contract as my Airbnb is growing rapidly and I feel like the extra level of protection couldn't hurt. 

Many companies require you to use their application forms (on-line or faxed/e-mailed), which we do and add our own supplemental pages for info they don't request but we want.Think about the qualities of a good tenant, what your criteria is, and design a process to weed out undesirables and look at credit, criminal landlord history.  

My plumber I use only charges $25 to set toilets but he is underpriced so I get a sweetheart deal - he has a good day job and this side money is to supplement his retirement   - I'll have to find a new one when he's ready to hang it up.  

It includes but is not limited to monies derived from Social Security benefits, supplemental security income, unemployment benefits, other retirement programs, child support, the Aged, Blind or Disabled Cash Assistance Program, Refugee Cash Assistance, and any federal, state, local government, private, or nonprofit-administered benefit program."

If you are looking to truly supplement your income, you are going to need to significantly raise your unit count.

Smartmove is the supplement after they pass your basic criteria.

So, to look at the untaxed income in the same light and with the same calculations, you should "gross up" the untaxed income 25%.So, when looking at 3X the monthly rent, you first add 25% to their untaxed income, then multiply that by 3.An example: In CA, SSI income including the state supplement, is $890/month.  

I can however say that the scenario you outline is not a wholesome one - agreeing to one rate and then paying some kind of supplement on the side.

With that being said as long as I have the rental income to supplement the mortgage, with a little extra wiggle room, to me its worth it to stick to your guns in the event of any market dip.