I had an option to buy a park up in Lincoln, NH and a guy showed up from the state of NH, encouraging the occupants to form a Co-Op, which they did, so I had to step aside.

What should you ask a co-host/property manager when they offer to list, market, maintain, and turnover guests for 20% of gross revenue?

You could be a "Co-host" without that requirement, which means you don't handle the receiving of money. 

He wanted Guy B as a co-signer, so we agreed as he had some income and met the credit requirements. 

We have been thinking of self-managing and maybe finding a co-host. 

As an alternative you could as for a co-signer on the lease with acceptable credit or only except individuals that meet a certain credit score threshold.  

I recommend having mommy or daddy  be a guarantor not a co-signatory.  

What you are describing is really just a co-signer.

Where to start... 1) You have a co-signer that you haven't vetted; 2) You offered a re-lease to them while they owed back rent; 3) You decreased your security by leaving tenants off of the new lease; 4) You provide 'excellent' housing services but yet are $500 lower than market (not understanding what problems that brings you); 5) You 'write off' back rent it seems sporadically and as you deem applicable (fair housing issue); 6) You have a Tenant that is 3 months!!!

@Will Walker if I'm understanding you correctly, you need a co-signor to help you with the 5% down on your primary home?