I usually wait 7 to 10 days then I start 
emailing the seller. If you paid for something 
on the 31st you should have recieved it by now. 
I would email the seller and ask how he sent it 
out, maybe he has a tracking number or something.
I recently dealt with a person that had a 
certain Cowboy Bebop Faye cel up on this very 
page for sale. After numerous emails to telling 
him the price was toooo high he finally sold it 
to me at a reasonable price. This person told me 
that the cel would be sent out that week,,,but I 
never got it...I emailed him back numerous times 
asking him what was going on and I found out 
that he sold me the cel without him even 
recieving it from Celga! Argh!!
I was upset and got my money back. 
So basically you should email the seller if you 
are concerned. If I never did,  would have just 
waited and waited for nothing.