Is it bad manners to fix a computer and charge a small fee?

i'm happy fixing comps for free for family and friends, but i'm sick to death of being expected to fix comps for friends of family or neighbours for free and they dont even have the decency to buy me or the missus a drink. honestly they think its easy to fix a comp, i've taught myself over 20 years how to do it. anyway on short notice i got a call from my sister could i fix one of her mates computers. thing was a piece of crap. i rebuilt it and had to va the whole case out. its now good as new. i told my sister to tell her mate 30 quid, i'll take 20 she can keep 10. my sis says she never told her mate there might be a fee. thats ok if your mate doesnt want to pay she can have her comp back as good as new but i'll never fix her comp again (her mates) or any of her other mates comps. they can bring them to PC world pay 40 quid before the comp is opened and wait 5 weeks to get it back (i told sis). am i being greedy or expecting too much?. thanks.