Last year when I saw the market way above the BG I committed to, I wanted to back out but had a guilty conscience. So I went to the BG and told him with 100% honesty what was going on and he pretty much understood and didn't really protest me backing out. For some context I did plenty of other ordering for him at the time (electronics and such).
Learnt my lesson for this year.. when I saw the hype commishes coming out, didn't commit anywhere, even silver.
Anyway, it can't hurt to ask, especially if it's a BG you deal with outside of coins. Just an idea in case you haven't tried the obvious.