Last year I bought an international money order from the post office for some KX parts in the U.S.
Once I notified the seller that I had posted it, then he emailed back and told be the parts were no longer for sale.
So I asked him to cancel the money order but didn't hear back from him.
I approached the post office and was told that I couldn't cancel it from my end plus I had to have the original money back to get some of my money back.
After a few choice words and threats, the seller did mail the money order back to me but it still cost me quite a bit.
btw this was actually an advertiser on this site (who I haven't seen advertise anything else since btw) so I didn't have any back up from eBay/Pay Pal etc.