if it's for an auction, i wouldn't send it through western union. if you send the payment, and the person never sends you your product, there is no way to get your $$ back. this happened to me before...i was stupid and really excited about what i was buying...and i lost a lot of money from it.
I've sent and received money internationaly through Western Union, the service is fast and safe, if the high errand doesn't bother you. Always a good experience, but I 've never use it for ebay transaction
I've just used it to pay someone today (!) from the PF, but I would be really hesitant if it was to anyone else. Pretty fast, it says the funds are available to be picked-up already and I just sent it an hour or so ago.