Yes it is a sale and typically there is sales tax involved on the sale of a vehicle. This would also be recorded in their books (accounting). There would be a complete trail of this vehicle when it came into the dealership as inventory while it was held and when it left. Along with any other transactions involving it - upgrades, etc. Not to mention every vehicle has an individual VIN number.
Even the high cost doesn't matter - think of a grocery store -- you go in you buy a pack of gum and pay cash. All this gets recorded via their books - think the item gets scanned when it comes in as inventory, costs get recorded, etc. and the opposite as it is scanned gets checked out. So if a buck in cash is going to get reported to the IRS, the $50k transaction certainly will not slip through the cracks.
Unless you are working with a shady dealership and then you all are likely to get into trouble.