Has anyone ever had a set of coilovers re-built?

I have heard talk of some motor bike shops doing it, or I know you can send them back to the factory for re-building. But I was wondering if anyone had accually done it? I have a set of tein’s I would like to re-build or replace and I am trying to figure out what would be cheaper/better.
I talked to a local bike shop and they acted like I was an idiot! “you can’t re-build car shocks, and even if you could I wouldn’t know how.”
Please share any advice or experience.
Thanks