And in the case when they were able to do it the process wasn't quick and straight forward, that is why Solera is my top recommendation for clients. 

It should be very straightforward if you have the proper guidance from a broker or lender.

Red flag- there business model seems straight forward.  

I would just suggest you make sure you fully understand that process before you dive into it - because you can lose a lot of money fast if you don’t know all the ins and outs.Likewise, rehabbing isn’t always straight forward… like who will do the work, permits, contractors, unknown damage you may not have accounted for - especially in  a foreclosure where there usually isn’t the ability to inspect the property.We’ve done several flips we won at auction, and lost plenty of them in the bidding.  

Where the letters aren’t outright fraudulent and lies, they are misleading, with the person selling or giving the proof of funds letter to the unqualified wholesaler doing zero due diligence on the property and at best stating that, technically, funds could exist and or be set aside for the purchase of the property,The practice, when used this way is meant to mislead, and those who ask for, give out, or receive, proof of funds letters in this way are not welcome here on BiggerPockets.The right answer here is to qualify for a loan on the property personally, and show this to a seller, or to be straightforward with the seller that you are in no position to buy the property personally, but will be wholesaling it for them. 

You will want to look out for a lender that is responsive, straightforward and has a track record of reviews and closings.

Regarding a refinance on a sub2, are there any special conditions or is it straight forward like a normal refinance?

If so, that is pretty straight forward. 

I don't watch a lot of fiction but happened to see that one.It seems this is straightforward and checker not chess. 

I have asked if they feel unsafe but I never get a straightforward answer which could be indicative of one of three reasons you stated.