There's nothing wrong with going to the dealership as a blank slate and asking the salesperson to just show you some cars.
But these days, with vast amounts of new-car information available online, dealers expect customers to come in having done their homework.
Americans usually buy their new cars out of available dealer inventory, so the one of the few ways to throw a dealer for a loop is to want something obscure or specific, in which case you might require a special order.
For the rest of us, if you head over to Joe Local Smalltown Toyota with designs on a 2019 Highlander Limited, but you don't want to spend more than $40,ooo and have a four-year-old vehicle with normal mileage that's been well-maintained to trade in, chances are there will be something for you to test drive. If not, then Joe Local Smalltown Toyota can arrange to have a vehicle sent to the dealership.
It helps to know what you want at the level of color, wheels, interior, and so on. But the trim-level is the bare minimum.
Knowing exactly what you want is something of a defense against an upsell. The Highlander Limited Platinum is just a few grand more than the Limited, but the dealer may have one if they lack a Limited. If you're financing, the extra cost can kind of disappear. But if you know what you want, you can avoid busting your budget in the heat of the moment.