To flip something, in this context, means to sell it.
And a VIN is a Vehicle Identification Number. It’s essentially the serial number of the car, with a lower number indicating an earlier production time.
So in short, Tesla will sue people who are trying to resell their early production model cybertrucks.
If it’s a long-term lease, like Honda did with their Insight hydrogen fuel cell cars, you could actually make an agreement something like this. But if it’s an outright purchase, Tesla trying to outright restrict resales is possibly illegal.
Unless they signed something that would prohibit the resell (like you cannot legally resell PlayStation developer kits, because they‘re still legally owned by Sony), yea, it’s their property. Nothing Tesla can do.