A few things:
Yes, the LMK line most certainly seemed like asking if he wanted to back out of this deal, and actually, very likely might be the reason we're discussing this right now.
The buyer actually agreed to paying no more than $480-490 ($450 plus $50-60, less $20). It didn't make sense for the seller to come at him for $3 more than what he quoted, just because he didn't want to eat another 3 extra dollars.
That, and his LMK wording, basically allowed this to fall apart.
Xela could have still taken a cheaper shipping option, I know I would have. And he could have been paying $11 for shipping instead of $43. So, he's still a righteous noob for not following through with his commitment to buy these books.
Going forward, bcc should also be careful of his wording. After a deal is struck, no more "Let me know if that is what you want to do" lines. Also, no more don't tell the guy $30-40 for shipping and then ask for $43.
-Andy