The seams should always be finished and sealed, both for looks, as well as to prevent moisture from infiltrating. Welded seams would be best of course and done properly, the look is amazing.

As far as fixing it, there is always a way to fix things. depending on your situation, the solution may come down to $$$. talk to the fabricator and see what he says. but if you ordered an L shaped, there is no reason it can't be finished properly.

In most cases you want to have a finished seam. If it's possible to weld the seam then that's ideal. Pending on the substrate (plywood, mdf, particle board)... you may not be able to weld the seam due to fire concerns. The other option is to run a silicone bead and flatten it out to ensure a water tight finish. The following site has some more information regarding stainless counters.

http://www.metalcountertops.blogspot.com/

Here is a link that might be useful: Stainless Counters

This is an old thread but I figured I'd add my $0.02. It is extraordinarily difficult to do a flat welded seam without causing warping in the stainless. And it is absolutely a bad idea to do after the countertop is glued down, due to fire risk. The best solution is to use gray silicone caulk along the seam. We do this with the countertops we fabricate and get a very nice look without risking the heat warpage that would come with welding.

They put a silicone puddy on my seam and it looks horrible.

We are not accepting this. They are suppose to be experts I don't see why this is even an issue.

We pay a lot of money to have it done right and they are trying not to eat the mistake.

Silicone putty is a bad idea. However, they could use a stainless steel epoxy which would end up looking very like the metal as it would have fine steel particles embedded in it.