I am trying to put together a series of books 1-6 of trade paperback.I ordered the exact isbn number for the trade paperback and I was sent the mass market paperback,a completely different isbn number.The member who sent it to me hasn't responded to me yet and it has been 2 days.

"Once you have marked the book(s) received, give the sender 5 days to respond.

If you don't hear from the sender within 5 days:

For problem books that were marked received and are now in your Transaction Archive: go to your Transaction Archive  and click the "Was Problem Resolved?" button.  Then choose "The sender didn't answer PM asking to discuss this."  This will send an email to the sender, making it clear that she or he needs to respond or forfeit credit for this swap.
If you don't hear from the sender within 2 days after you have done the above to send that "follow-up" email to the sender, contact us.  Failure to respond (in an active account) is considered admission of fault in a problem swap."

So, you would want to give them the full five days to respond, and if you still have no reply, follow the instructions above.

Is that a new option "The sender didn't respond to PM...?"  I hadn't seen it until lately.