#1: You won't have the option to considering I won't be selling any Legos anytime soon.
#2: I agree though, if you paid $70 and the set was advertised complete, you shouldn't have had any issue, but that still isn't a reason to leave negative feedback, neutral is better.
The flag with the Falcons symbol runs $8- $10.
Call me crazy, but that's not really as much as I expected you'd say... sure, I wouldn't want to pay that much JUST for a fancy flag, but if I were in your situation and it was to complete a collector's item, then it's really not that much money compared to if you had a decent paying substantial salary, $8-10 isn't really that much to just throw away. I mean, it's not like you can't afford it.