Can you refuse the adjusted offer and keep your car?

Yes. If Carvana reduces your offer at pickup, you are not obligated to accept the new number. You can decline the sale and keep your car. The inspector will leave and the transaction ends. However, if you have already made plans around the sale (like purchasing another vehicle or arranging insurance changes), the disruption is real. This is why getting competing offers before scheduling Carvana's pickup is important.