What do people think of buying overcoats on ebay? I need my first db overcoat and I'm thinking of http://www.ebay.com.au/itm/HART-SCHAFFNER-MARX-GOLD-TRUMPETER-DB-Over-TOP-Coat-CASHMERE-Trench-Jacket-38-L-/360694620142?pt=US_CSA_MC_Outerwear&hash=item53fb131fee
My suit shoulder to shoulder is 17".
I've bought several overcoats from eBay, including my absolute favorite, an old PRL double breasted guards coat that weighs like 15 lbs and is super warm, and looks like it has never been worn. Didn't require a single alteration to fit me spot on. And I paid $60 for the thing.
As will all things eBay, you just need to 1) know what you are looking at--cannot always rely on descriptions, 2) know your size measurements very well, and 3) even if everything looks perfect, know that sometimes things won't work out. For example, I bought a coat once that looked great, fit well, etc, but was just a little long in the tooth. The condition was not such that I felt like I could return it for incorrect description--there were no holes or threadbare spots--it had just clearly been worn hard and didn't have much life left in it. Accept that this might happen and move on.
Also, know that it might take some time to find what you are looking for. I stalked overcoats for a good six months before finding that PRL guards coat I love so much.