without having to tell you or ask you what is wrong with the door and why it needs to be replaced, ill tell you to just replace it, yourself.
go to home depot, and ask for a PRIVACY KNOB SET, it is a
An interior lockset.
Designed for privacy rather than for security
Has a locking button on the inside knob but no key device on the outside knob.
Can be either a knob or a lever.
In an emergency, the lock can be opened from the outside by inserting a narrow object through the small hole in the outside knob and either depressing or turning the locking mechanism inside, depending on the type of lock. "
for more info on it, go to
http://www.doityourself.com/stry/typesofdoorlockswhen you buy the new locks, all you have to do is remove the old one with a PHILIPS HEAD SCREW DRIVER, and the same for installing the new one, a new lock set will run about 15 to $20 new. much cheaper than a locksmith. just read the directions that comes with it, and youll be set.
i have no idea why your lock would not work, theres just a latch, and/or a dead latch, depending on the lock, and maybe the spring is broken. if he was a really locksmith, he would have just replaced the spring to the latch or fixed it in anyway possible for ya, with the inclusion of picking it open. i would have atleast.
if you have any more questions, there are plenty more qualified locksmiths on here than me, KOKOMOLOCK being one, FARMERFREAK, and several others, you can always ask them but i think this will be the best route for ya. good luck