Not an LBS fan, but doubt the LBS is to blame. No off the shelf bike comes with wheels for your weight. 300lb SYSTEM weight typically is the limit. Even if you were under that, a shorter life is expected. So no one ever could sell you a bike unless you are willing to spend $ on custom wheel.

What would you have said if they refused to sell you a bike because of your weight? See.....

A 36 spoke triple butted spoke would be my recommendation.

I don't understand what the RD has to do with weight.