I just got my car back from the body/paint shop and there are several runs/sags and a lot of junk in the clearcoat. The painter claims that he can fix this in my garage. Since I don't know anything about body/paint, I'm seeking advice on how best to proceed.

Can it be fixed ??? Yes....But usually the shop will sand/buff the car before it ever leaves their building... .. What kind of arrangements did you make before the deal was done???What choice do you have but to let him deal with it ??? Don't take this the wrong way but most reputable shops won't consider letting anything like that get out the door...Don't let him drag his feet or start another job... Make him get on it right away if you're going to let him do it in your garage..

it depends...

I had all kinds of problems with mine, and after a cut and buff I am quite impressed with how it turned out...

Not perfect, but very nice for a first timer...

I need to buff it again to get some cutting scratches out, but I will wait until winter for that too busy

I had some runs in the clear on my mustang and made the guy sand and fix them. Came out good, but he was kinda angry that I pointed them out. I could have fixed them myself, but he's the one getting paid to do the job right the first time.

What kind/type of paint??

Lots of shops pull this routine..They let it slide and hope you won't notice becuse they don't want to do the cut and buff.

That being said... I HAVE seen alot of bad jobs turn out nice after a cut and buff.

I'd make him fix it with the understanding if he screws it up he's fixing it on his dime.

Give him a chance to color sand and buff the car and then reevaluate it. Color sanding and buffing can get a lot of stuff out of the clear coat as long as the junk did not get it the base coat.

Also, be sure to check that he does it down low at your rockers, bottoms of doors, etc... I have had guys shortcut because it is a pain to do it right down there.

why would you even pick up the car in this condition? I hope you didnt pay more than few hundred buck for that half-a$$ job

The longer they wait the harder the clear is to cut and buff. I've always done it within a couple days of spraying it.

I would have never accepted the car like that.

Chally1 is correct about cure time; even 2000-grit wetsanding scratches are hard to get out if you let the paint fully harden.
Check the paint down low (rockers, etc) to make sure there's enough there. Some guys just don't bend down and cover those areas enough, so if it looks "dry", fixing any runs (and it's possible to have both) will burn through.
Also consider what texture you want; factory texture did have a little "orange peel" - not as much back then as nowadays, due largely to current EPA-legal solvents - so nibbing & buffing areas dead smooth will look weird compared to a "normal" texture surrounding those areas.
There's a LOT more to painting than most people know, including - unfortunately - many "painters".

Hello:
Defintely make him fix it. Paint jobs are expensive (for good ones) there is no reason to accept shoddy workmanship.

Maynard