Whats the procedure for postage when you pay $8.00 but when the goods come the postage is only $2.10

[pookie1m]

Hi There

Whats the procedure for postage when you pay $8.00 but when the goods come the postage is in an ordinary envelope and has stamps to the value of only $2.10?

Should the seller reimburse for the extra postage or is that how it works?

Regards

M