We need more information.
- When did you make the payment?
- Has he/she been very active on the boards but just not replying to your PMs?
- Did you pay with a credit card via Paypal?
- Were you thorough in your payment notes in Paypal?
From time to time, emergencies and other priorities arise. I try to ship items out next business day or at least generate the shipping label so it forces me to have to package the items and slap the label on it, but things come up and I can't make the post office that day. Airsoft isn't a #1 priority for everyone.
If it has been over a week without communications, I would begin to worry.