It never fails to amaze me that people will ask other people to do their jobs for free, for them! I know a couple of people who took training in, say, massage--and now their friends expect free massages. Which isn't to say it's not totally awesome when someone DOES offer to do it for free, but the key word is 'offer'. Though apparently it happens to all jobs...someone once said in aggravation 'What, do people go up to lawyers and ask for free legal advice?' and a lawyer responded 'actually, yes!'
Also, who are these people who don't take no for an answer? For me, if I ask someone for a favour and they say no, I"m probably going to be too embarrassed to ask for something similar for awhile, feeling I've overstepped.