Quoted from xTheBlackKnightx:

This is not "odd", it is called seller's remorse, and an additional lack of preparation by the buyer.
Foremost no agreement of any kind, verbal or written.
Blaming the seller for not wanting to sell under these conditions is not the fault of the seller.
Everybody's time in this case was wasted, not just the buyer.
I have had people try to buy their games back from me, including directly on site after loading!
Learn from this experience.
Learn from my significant experience.
The proper steps of onsite private owner buying (not dealers or brokers) unless extremely close in distance for a simple courtesy inspection:
1 ) Negotiate the final price beforehand, and be prepared close the deal upon arrival.
2 ) Establish rapport on arrival, initial greetings, and unload your tool box (shows serious intent to buy), but do not bring them in the house except a flashlight as that can be unnerving for some owners initially unless you ask them first!
3 ) Conduct a final technical inspection of the game for any major deficiencies or omissions, ask any necessary questions, but be brief
4 ) Have two printed professional invoices on hand at time of pickup, and notify the owner will sign them
(I normally provide an "unofficial" copy of the invoice via email beforehand to the seller to verify intent to buy at the negotiated price, as it makes you look serious, responsible, and professional, if they waffle, it is time to reconsider your options now)
5 ) Have the owner sign the invoice in duplicate and you sign as the buyer with full responsibilities after inspection, and give one to seller for records
6 ) Pay for the game IMMEDIATELY
7 ) Have the former owner count the money (if applicable, but highly recommended method of payment)
8 ) Load the game!!! (Repeat this to yourself 3X)
9 ) Be prepared to leave with courtesy, if the owner starts getting game memories, as it is now YOUR property.
10 ) If you have a business card, this is the time to give it out
11 ) Thank the owner for their time
12 ) Leave, and go get something to eat for the drive home
No BS, do not skip any of the above steps.
This eliminates nostalgic sellers from deciding to back out.
This prevents "wishy washy" sellers from changing their mind.
Changing your offered price on site is a "no no" if a price is conferred, unless there is something seriously wrong with the game. This is commonly called "undercutting" (not lowballing) in the market, if the game is as described and is a common tactic of flippers. It will anger owners in the same manner as asking if another game is for sale out of collection while in site. Don't do it.
Take the personal "pinball tour" later, if so inclined and it works out, and things are friendly.
Business first, except to establish added rapport.
That was one of the problems here, you gave the owner more time to "think about pinball life".
There were multiple errors from both parties, because everybody was trying to be nice instead of being direct.
I recommend this post be tagged, as this corrects most common errors regarding sales especially regarding invoice omission.