Also worth pointing out is that it's not just the sale price that determines whether it goes out for authentication or not, but rather the listing price. So if they list a card at $300 BIN with a Make Offer option, and you offer $150, it will still be sent out for authentication. I just had this happen to me on a card that was listed at $499. I offered $85 and it was accepted. Then, it shipped off to CSG...
then back to me.