I think they are trying to drum up business. They are all hurting, looking for any bull to charge you for. Way high prices too. Look in the glove box changing your own filter takes like 5 min tops. What they are doing borders on criminal. How do they know it has carbon buildup? Have you complained of knocking, set codes? Carbon causes hot spots, will cause knocking. Do you have a funky smell? No, then no air filter for me.
Tell them politely no thanks, that is what I would do if I haven't had any previous issues. I have two cars with over 200k never had fuel system flush. Just a can of sea foam in the gas with every oil change.