User Activity

I am an individual (not a store) based in Canada. Just sold an item (used, not new) to someone in Texas. I see a USD$40 charged (and payed by buyer) in the payment confirmation. How do I deal with this ?? It's the first time I get this (out of about ...
Can someone explain how this can happen : I listed an item in August. Got an invoice of $1.89; Item sold in September for $42.00 : paid another $3.01 invoice Then on October 31 I get a third invoice, this time of $9.67 This makes it $14.57 for an ite...