I presume that you are looking for clues and cues regarding big problems that others cannot or are unwilling to resolve themselves?

Also renting out a condo can be frought with issues if you have an unwilling HOA.

If they are unwilling, move on.

That's it.In order to do this, you are looking for problems that others either can't or are unwilling to solve themselves.

He is not willing to move up the closing date as he WANTS to be at the closing and he "already took the day off of work and is unwilling to change it". 

If you are unwilling to pay that amount, you are probably chasing a lost cause.

If they are unwilling to provide you with references I would not consider investing with them.It's not uncommon for house flippers to borrow money and pay high interest rates (12% or more).  

Also if the bank is unwilling to work with him, because he does not have a hardship then they sure as heck are not going to work with you.

If the tenant is unwilling to complete one (or the seller is unwilling to present them to a tenant for completion) . . . then this tells you something and you may want to further investigate as it is a red flag.  

(we have a lawyer involved in the ejectment case against us and he has no idea why they are even trying this route because they have no case as all the paperwork was done correctly)  However, the investors are seemingly unwilling to extend the lease so once the ejectment case has been thrown out we can continue with getting it all complete.