If the seller has good feed back give him 24 to 48hrs,
if nothing you can cancel just ensure you don't leave
a review yet because that will close the chances
of getting your funds back.
Truth is, sometimes it happens, it happened to my instagram gig just few days
back. I had it set for 4 days and delivered empty gig after 5 days due to technical issues
and sent them a mail promising to fix in 24hrs or give them a refund.
I still couldn't fix in 24hrs and all my client cancelled.
However, after it was done, i still delivered the service without any cost.