I feel that it would always be wise to attempt
to contact the buyer....it is possible
that he did send the money and it either got
lost or you confused payments....there
are several things that could have gone wrong..
he/she may have just forgotten that transaction..

I would also suggest that in the future you
keep the buyers email and address handy...
I always put it with the chips...until the transaction is resolved....

Communication generally solves most problems..