Yeah.. I'll be wary of this strategy.. Only do this if you have funds to cover the surplus. But given the size of the demand, generally if you don't want the allocation, I'm sure your broker can reallocate that to someone else easily.. But make sure you do have a chat to your broker before hand..
My broker generally pretty good.. I've always get between 80-100% allocation in the past (Healthscope, etc)..
