If they have the ability to purchase the note, why can't they just buy it directly from the bank?

Those companies you asked about are more for deal finding and direct contact to off-market sellers, is that what you are looking for? 

When I asked the seller for receipts detailing the work done and requested permission to speak with the mitigation company directly, he refused.

The problem (as you have cited) is trying to understand what you need (you don't know what you don't know), where to get it, qualifying its source(s), and the validity and usefulness of all that.Pardon me if I've gone into this too much, but I meet many people with the same concerns that you are voicing and this is offered, as much as possible in direct response to your post.Please feel free to contact me if you have any comments or questions. 

That said, utilities that aren't directly attributed to a unit can be a pain in the neck because everyone is sure that the other unit(s) are using more power than they are.

Potential for manipulation: Some agents may be using this argument to discourage sellers from allowing buyers and their agents to negotiate commissions directly.3.

So there's not a way to know unless you find out from the seller directly.

On the surface that sounds fine except with VRBO I did not where I have access to their credit card to charge them directly but rather I could submit an extra charge and it's up to the guest if they pay or not.

If you get a plumbing bill for $100, that $100 goes directly to the plumber. 

You can also list on Facebook Marketplace, join local Section 8 Facebook groups, or contact CMHA directly - they often have a list of people looking.