It partly depends on how the shaft got warped.
If it was left in a hot car or car trunk, then the odds are good.
If it is a non-maple shaft and/or it came from the Phillipines, then the odds are not good.
Also, if it has an "S" bend - especially in two different directions/planes, then straightening is unlikely.
Everything else is in-between - I don't charge much and if I can't straighten it and keep it straight, then no cost to the customer. Of course, they always have the option of ordering a new, custom shaft from me.
In general, I have been successful - and I got tutored my ManWon (via email/PM). He's been a REALLY helpful guy.
My 2 cents,
Gary