This happened back in the mid 70's. We really weren't sure the bills were real. The bank wasn't sure at first either. Like us, they thought it was a bit fishy.
I have been searching on how to buy an expensive vehicle with the least amount of hassle and found this article. It is a blog-vertisement (Advertisement masquerading as a blog) but looks like an option for vehicles. I bookmarked it for later use. I thought others might be interested and/or use it as a starting point for their own research.
https://privateauto.com/blog/5-safe-ways-to-transfer-money-in-a-private-car-sale