It doesn't look like the 2 pieces fit well together. I would be very concerned. I'd withhold payment until it was fixed or the pieces replaced.

Yes. Be worried. That looks awful.

What ever happened? Did they turn out better?

Here is a link that might be useful: Mt granite installed

the corner joint is horrible. however, it's obvious the parts are not yet set so they may be fitted together much better before they are done. As is the inside corner joint is completely unacceptable. the fit around the wall is not horrible if properly caulked in and its completely acceptable if its going to be covered with splash.

It doesn't look good.

Below is a link to the Marble Institute of America....

"For over sixty five years, the Marble Institute of America (MIA) has served as the authoritative source of information on standards of natural stone workmanship and practice and the suitable application of natural stone products."

On the link has drawling of seams and locations of how they should be placed, and how tight, and smooth they should be.

Here is a link that might be useful: Marble institute of America....

Wow! They're not off to a good start.
But what matters is how the finished job turns out.
MIA is just minimum guidelines, competent fabricators will surpass those guidelines.

I just saw this. Did you get it corrected? I work for a fabrication company. We do not do 45 degree corners as they are too thin at the edges and tend to chip which it seems yours did. This is awful. I sure hope you got it corrected.