I've been demo tying at IFFF shows for almost 30 years and agree with all the advice given by all above, but would add to Rick's comment (Hello RicK!).
It should not be if you give them away, but rather when you give them away... (and I know that Rick does generously hand his flies out to the show attendees at Federation shows).
IMHO, as a demonstration tyer (of whatever skill level), you should always give away every fly that you tie when people are watching you at a show!
That simple gesture of handing that fly to a person who may have traveled hundreds of mile just to watch folks such as yourself tie, will make that individual's day/trip... Such flies are often kept for many years
The gift of that fly will bring enjoyment that is without measure. Whereas, if you end the tying process by saying that they can have this fly for $, it will leave that same individual with a very different opinion of you, the show and his whole trip...
Glad you had a good time tying. Hope to meet you a show someday!
Kyle Moppert
President
Gulf Coast Council - IFFF
Lifetime Member - International Federation of Fly Fishers