I do a little consulting on commercial negotiations but in all negotiations there are principles and behaviours that are important to know. Probably the most important is knowing where the balance of power lies between you and the seller (In this one I suspect it’s with you)

After that...

1. Know the type of negotiation you are going into... after the deal is done will there be any financial or personal relationship between you and the seller. I suspect not which means that you are going to have a negotiation grounded in hard bargaining or bartering
2. You can’t do too much preparation
3. There is no such thing as ‘fairness’ in a negotiation. In these types of negotiation your best result is the lowest possible price - no matter the impact in the seller
4. Have what is called a BATNA... best alternative to a negotiated agreement....the seller needs to know you have options
5. Unfortunately he has played the first card and preconditioned you with his opening price. It’s too high which is a classic tactic. Your opening offer needs to be equally extreme on the opposite side. You need to get into his head and have a good idea on what his ‘walk away point’ is. You will of course know your own walk away and between those 2 numbers there will be a deal to be done.
6. Be prepared with the things you’ll ask for as conditions for moving your price towards his - there will be tons of variables and your preparation should identify as many as possible (know the ones of highest value to you and lowest cost to him and vice versa.... that way you’re always playing your cards with insight)
7. Even though it’s one of the variables know that ‘time’ is probably the one you can use to exert most pressure