personally, i make my setups from scratch, not by modifying inferno sets, so it feels good when i finally come up with a set that doesn't suck, and i think that people who only ask for other's setups and don't make their own are missing out on a really fun part of the game.
nonetheless, i will share sometimes.
if i'm spectating and see someone who is making a good effort, but is obviously held back by a bad set, i will ask them if they want to try my set. similarly, if i see someone i know who normally drives a different car who is trying out the car that i drive, i will offer my set.
when people ask me politely, after a race, and have done a few laps on the server to show that they aren't a wrecker, then i will usually send it to them.
but i wont respond to people who ask during a race, who aren't polite, or if they can't demonstrate at least some skill. if you are crashing at every turn, practice will help you a lot more than a different set.