I'm having the same problem with another inworld store owner. I tried to buy a skin on 8/16/16, but instead of getting the item, it said I failed to pay the owner/creator but took $1500L.
I IM'd and wrote a notecard that day. No response.
I wrote another addition to that notecard, saying I wanted a refund or the skin I paid for, noticing she had been online that day, so I know she saw my nc. No response.
This kind of behavior should be handled by SL as FRAUD if these creators refuse to make good on a purchase. It's STEALING from other residents
***SL/LINDEN LABS - if a resident complains about paying for items and not receiving them after 2 days, then YOU should be reimbursing those residents. It's easy enough to look up the paid for & received items in an account.