I believe the housing shortage and low vacancy rate is a bigger influence.  

I'm wondering what avenue most investors have used to have greater influence in a negotiation. 

I love Dale Carnegie's negotiating advice in "How to Win Friends and Influence People."  

Typically, can you influence the appraisal by coming to the table with selected comps of your own, or is that something that you're stuck with whatever loan provider you're getting the refi from?

Stick with it and you'll figure it out.Read books on sales & networking like How to Win Friends & Influence People, Crucial Conversations, and What They Don't Teach you at Harvard Business School.You'll eventually meet people who'll tell you to drop out of college.

If you provide it, you may become responsible for your guests actions while under the influence of it. 

The variables that influence the expense ration tend to be the type of park, the amenities at the park, the utility solutions, and the onsite required staff.  

So, if you can not influence one of these items it will not make a difference. 

You will be influenced by today's financials needs (greed or fear) and instead should formulate a policy for accepting tenants beforehand.

It helped influence my process to make sure I know the previous owner is either deceased or has accepted the foreclosure.