If the seller explicitly agreed to hold it a week, then to do otherwise is lying - I’d have to agree with the buyer. I hold honesty and integrity in the highest regard.
If the buyer wanted to inconvenience the seller to wait a week "for free" thinking that he has earned some goodwill so deserves this special period, then I agree with the seller.
For the seller, it’s better to have cash now to move onto other things, than to wait later with the increased risk of non-performance.