I have a hard time believing the lbs would hint that your bike is unsafe. You'd think they'd tell you something like that in no uncertain terms, or at least indicate what they worried about. You could come right out and ask them if they think it's dangerous.

I guess that doesn't make it fit either way.

With your size, if you cant' find a used one, maybe you could get a low cost Bikes Direct bike and make some modifications to get you want you want within your budget.