Sweeten the pot one might say 

How could I sweeten the deal for the cash provider?  

It may be hard for the next 30+ days while they rant, rave, and try to make your life miserable, but then they will be gone and you will immediately notice your stress levels go down, you will free up a lot of time, and everything will be better.P.S. this is one of those situations where you may want to sweeten the pot.

It is common to offer above asking price to sweeten the pot as many owners would simply rather collect the cash upfront.What makes it a desirable offer structure?

I may even sweeten the pot and offer to pay them a few thousand to help them with moving costs.

What I'm saying is, throw a little sweetener into the coffee.You also say there is some sort of signage issue from a neighboring property.

It doesn't have to be that way--you can give whatever equity you want for the money you receive, sweetening the deal for you or the investor.

You may want to sweeten the pot by only charging them for some of the equity (e.g. $10,000 instead of the full $20,000).

Whenever I've done seller-financed deals, I've offered something a little more to the seller such as a higher down payment, higher interest rate, quick close, reduced contingencies etc. to sweeten the deal beyond a normal sale, and I've shown them proof of funds that I can pay off the property in cash, so that helps give them peace of mind that I'm a credit-worthy borrower.

Presumably the tenants payments would allow you to save a chunk towards the second tranche, if you will and you have that time to earn, borrow, etc. more cash separately. 6% is a very good rate right now so I’d sweeten the deal with a pre-payment penalty, say 3 years?