In answer to your question know, they only offer the good but at rip off prices selant eg Diamond Brite, Supargard, Lifeshine ect. A dealer just usually cleans it and takes off the transit muck and nay protective coating the car may have. I know of people who have refused to let the dealer wash or prepare the carpreferringto clean it themselves.
Best thing is to give the car a good was and wax when you get it home. Autoglym HD wax if you want to spend a wee bit or Autoglym Gloss Guard if looking for something a little cheaper. There are plenty of others but these are easily brought from Halfords and do a good job.