He wants your mags AND your money?
If he is overpaying you with some sort of cheque, then make sure you are paid in full, & that the funds actually reach your account before you part with ANYTHING.

There is a scam going around where a buyer send an overpayment in the form of some sort of dud cheque. You send the surpluss somewhere then find that your payment aint worth a brass razoo.

The simple two step process.
1. Get paid, make sure funds are secure in your account
2. Complete transaction. Deduct any legitimate out of pocket expenses. Honest traders will understand & will wait, crooks will pressure you to move quick.