Refinishing over varnish

[mjet]

There's a Mustang Bass neck & body that I've been following on the 'bay - I've got some of the other parts for this and I might be able to make something interesting for a reasonable price.

Here's the issue. It seems to have been varnished at some point. I seem to recall that a luthier buddy of mine told me that there were some kind of finishes which soak so deep into the wood that it's hard to remove it (or that you can remove it but that new lacquer doesn't bond well to the wood). What are the hard and fast rules about this - are there some finishes (either lacquer, shellac or varnish etc) which are generally "too far gone" to do a good refinish? Or is everything a crap shoot?

[vegasrock]

...........

[mjet]

So it's not a lost cause entirely. Good to know.