They made enough money, but without a credit score, her grandmother offered to be a co-signor.

Other options could be finding a co-signer. 

It came from a co-worker who keeps tabs on several markets.

We are actively using the co-host feature on Airbnb, but upon reviewing the actual Airbnb terms and conditions we found the following terms:As a Co-Host, you may only act in an individual capacity and not on behalf of a company or other organization, unless expressly authorized by Airbnb.If we need to act as a co-host in an individual capacity we lose the protection of the LLC.  

Or they don’t do a good job screening.I had a co worker just go through that.

So since he was a co-owner, he didn't get notice and the judge kicked the case and restored their ownership despite the Tax Sale and one party getting notice. 

25% is standard as a property manager. 15% for a co-host.

Or for the "Go Getter" types, would you recommend not joining a co-op? 

I have the following blurb (for this exact same issue) as an addenda item in my lease that was also acknowledged and signed by them;"Resident acknowledges and agrees that this is a co-ed (mixed gender) and co-living house. 

Hi Bigger Pockets Community,We run a co-living and working company called Neighbourgood and are looking to acquire multi family assets, guesthouses and hotels in Miami and other lifestyle cities that offer value.