And you should go into the dealership with clear alternatives to each.
There are lots of dealers to buy vehicles from, lots of people to sell your vehicle to, plenty of alternatives to "add on", most of which are unnecessary, and lots of banks and credit unions to loan you money.
When you have alternatives and can use them at the dealer, you'll get dealership down on prices. Understand the incentives the dealers have (how they make money, especially extra money), understand their cost structure, etc. and you'll have even more bargaining power.
For example, you can often leverage financing to get the price down. The dealers get extra cash by bringing financing deals to their partners, so they might take a few hundred off the vehicle if you finance. Even if you want to pay cash, take the financing (make sure no origination fees or early payment fees) and pay it off before it accrues any interest.
I've also walked into dealers before with print outs of the same vehicle priced lower at other dealers and magically they become more flexible. I've ever tried this before where I didn't present this info and they let me walk out of the store, refusing to budge. Then when I came back with the info, they became more flexible.
The service departments pull this nonsense as well. I've negotiated service prices down 40% in the past and know that you can use things like recall repairs to get a better deal on repairs you actually need done (if you do x repair for $y, you can do this recall repair as well).
I think dealers are an extremely bad component of the vehicle market, but eliminating them will lead to people who can exploit the system to pay more. It will be an overall net benefit for the market though.