Private car sales/buying etiquette

I’m new to the private car sale/buying scene so this question may come off as naïve to those who are experienced in these but I figured I should post to anyway.
I’ve found a used car that I’m looking to purchase through a car forum, and contacted the seller last Wednesday. The seller is about 4 hrs. drive from me and has the title in hand. We corresponded via texts and phone calls throughout Wednesday and Thursday and he’d provide lots of details on the vehicle. I made an official offer on the car Friday’s night and he agreed to it (text). He mentioned that he’ll need to take the car in sometime this week to get the front tires replaced before selling. I asked if he’d be willing to get a PPI if I pay for it. He said yes, and texted me on Monday that the PPI is scheduled for Wednesday this week. He’d also let me know that he’d taken the wheels off the car and dropped them off at the tire shop to get the new tires installed. I’d let him know that I have the fund in hand and ready to drive up and see him whenever he’s ready to go.

He texted me today stating that the wheels may not come back in time for the PPI on Wednesday, and asked if I still want/need the PPI to go forward with the deal. He also stated that, someone else had contacted him about the car he would be showing the car to this person on Wednesday. I was taken back a bit since I thought we had deal and I was just waiting for the PPI. I responded back and let him know that I won’t mind if he put on the spare/winter wheels to go get the PPI while the main wheels are not back yet, but I would need the PPI to go forward the deal. Am I expecting too much that a seller would hold off showing a car if a deal is being worked on? Or is it fair game to show the car since money has been exchanged? The car is an exotic and it’s out of warranty so I feel that PPI is necessary.