It is very important that Dura-Ace bottom brackets be installed while the faces and threads are perfectly parallel. If it is installed into an out of parallel BB, it may be ruined and unusable. The new Dura-Ace BBs are very touchy.

In other words, the guy may be right in a way. The frame may be just fine for a different type of BB such as an Ultegra or better yet a Phil Wood BB that is Shimano compatible.

Since the guy has been such a jerk about it, I'd cut my losses and try out another BB in the frame. You should also be aware that your LBS may have contributed to the problem by the installation. If you have faith in them as mechanics though, you should consider buying a frame from them in the first place, it may be worth the extra expense to buy from them rather than try and save a few bucks using mail order.

As a fomer bike shop manager, I know how it feels to try and compete with mail order and then try to cover for a customers frustrations. There's a lot to be said for developing a good relationship with a good LBS.