Sure you can, but in most cases you would get a signed contract and probably put some money down to hold it. Once you find a vehicle and negotiate a price, you can ask.
Only the sneaky dealers will try and sell the vehicle while your waiting if they can sell it for more. That's why you get everything in writing.
Without a big deposit and a signed purchase agreement they will sell the car to the first PAYING customer.
Do not make a deposit to hold a car with any dealer or dealership that you are not familiar with.