Why are the speedmasters on the bay cheaper from Japan? Seems authentic. The model I'm looking at is the 3570.50.
Part of it could be that the Yen has slipped almost 20% in the last 3 months against the US Peso http://www.xe.com/currencycharts/?from=USD&to=JPY&view=1Y If they're still pricing Speedmasters based on local prices and you can buy Yen 20% cheaper it could start to look quite competitive. Its actually slipped almost 50% since 2013 according to the two year chart which is a lot more than I'd expected. Here in Australia we've gone from $1.10 against the USD to about 80c, pretty big drop but if you went mad buying up watches from America while it was high (some of us did... not because we're savvy currency traders... just because we have low self control) you're nicely ahead now.
Exchange rate as dsio pointed out, also it does not seem that used luxury goods do not hold their value there too well unless it is vintage or antique.
Depends on the seller but yeah it is safe just careful on customs and overall condition as if any issues you have to ship back.
I have purchased a couple of watches from Japanese eBay sellers. Just google them before you purchase to get a good idea from the sentiment on the watch boards.
+1. Stick to the reliable Japanese speedy sellers and you should be all right. I bought my Broad Arrow from one of them 2y ago and it went very smoothly, condition was in fact better than described. A fellow WIS who has a Japanese wife says the Japanese take very good care of their watches, so their pre-owned market is dominated by near-mint watches.
Some of the favorites from Japan are listed here http://omegaforums.net/threads/Ωf-unanimously-favorite-ebay-sellers-list.3612/
I bought a Speedmaster reduced from a recognized used watch store in Japan, no issues whatsoever. PM me if you want details.