This guy has taken almost a month to mail my cards. He said it got stuck in the machine and sent back to him and he'd mail it out again, but he's stopped responding to my messages. At what point do we give negative feedback? It shouldn't take a month to receive the cards unless he mentioned it would take that long in the first place.

You MUST file a Bad Trading Report (BTR) first. For rules on BTRs and more details, see here.

jmigliore wrote:At what point do we give negative feedback? It shouldn't take a month to receive the cards unless he mentioned it would take that long in the first place.

Never, without prior authorization by a moderator. First, you need to head on down to the Bad Trading Reports subforum and file a report there (make sure to include a link to the trade page, and a copy of the chat log. If these aren't included, a moderator will simply tell you to include them before moving any further.) Then, the deckbox team will contact the member. If they don't respond after seven days, you will be given the go-ahead to cancel the trade and leave negative feedback.