The biggest thing is the weight of the wool. A quality jacket is of a lighter weight wool than most of the poorer quality stuff and it's visually identifiable once you've seen it. Hand sewn button holes & hand sewn in general is also an indicator. There are several vendors mentioned earlier in this thread that are certainly museum quality.
I've owned several sack coats a frock & a shell jackett over the years. My first was a good quality machine sewn sack coat of a civilian pattern of correct materials but machine instead of hand sewn. My second coat was a poor quality shell jackett was not so good as was my second sack coat (I tholught I was upgrading), both mainstream quality which I sold off at my first opportunity. My final Sack Coat was made by Matt Caldwell via Waumbaugh & White... it's museum quality, all hand sewn and IMO as good or better than any other and all but indistiguishable from an original. I also own a Frock made by Jarnagin before their quality began to slide. They are dramaticly different jackets and put side by side only one is truly authentic w/ the the rest sliding downward in quality.
All I can say is to take a look at the offerings by Waumbaugh & White, John Wedeward (sp?), CJ Daley, NJ Sekela etc. They look different than the lower quality items. A different look to the materials and they certainly wear differently.
My sack coat is from a Waumbaugh & White kit, which my dear wife completely hand sewed for me. While there was a great deal of disconnect between my wife's knowledge of patterns and Dan's instructions, Dan took the time to answer all email and phone questions. I now have what looks like an original sack coat with one minor variation; instead of the standard interior pocket, which is visible on the front of the coat, my wife made a pocket using some old scrap navy blue cotton, which attached to the liner and is approximately two times the size of the original pocket. She maintained the same design, just changed it up slightly as it really got her goat that anyone would have left visible stitches from the pocket on the exterior of the jacket. Another slight variation is the stitch count; she averaged 18 stitches per inch (varied from 16-20 stitches per inch.) To me and the guys in the unit, it has the appearance of machine stitching. I myself would not believe it was not machine sewn unless I had not witnessed her work first hand.
She also has made many of my shirts, using patterns and materials from Abraham's Lady in Gettysburg. I usually carry three shirts with me to an event, just in case of biblical type torrential rain, such as fell on Saturday at Maryland My Maryland this year.
I have two dressed Hardee hats, one Dirty Billy and an old knock around for inclement weather when doing ceremonial or early war events. My forage cap is a McDowell style from James River. My frock, scales, dark blue trousers and leathers came from Blockade Runner as did my Brogans, which I have had double soled subsequently, by an old gentlemen who asked me who I inherited my brogans from. A great pair of brogans, with arch and flush mounted heel plate, very comfortable. Blockade Runner seems, in my experiences, to strike a good balance between quality and cost. The stuff I have purchased from them is of better quality and cheaper price than most of the big bulk sutlers I have seen.
My light blue trousers are used, of unknown origin.
My splurge is my number one blanket, a Filson which weighs about 10 pounds. I also have an issue blanket from one of the vendors in Gettysburg, do not recall the name off the top of my head. Great blanket for summer, but about a foot too short for my 6'-4" frame. Haversack came from a one man band vendor at an event and is an exact replica of the original regular army issue. I carry my grandfather's straight razor to complete my kit.
I have had my eye on a number of CJ Daly pieces, who seems to show up at just about every event I go too. I do need a great coat and do not know if I can risk having my wife giving me the business about making one from Charlie Childs or not. If that is too great a push, I will probably go with Chris for the great coat, but wonder if we will ever seen any weather cold enough to warrant the purchase. In my unit, the 3rd US Infantry, Nick Sekela is the recommended vendor and a number of the fellas have both complete kits from Nick. Excellent workmanship and materials, but a tad slow on getting the items out. He is not cheap though.
I have been giving some thought to doing a Confederate impression as well (I am ducking the imaginary bricks my wife is now throwing my way.) There is a young man I found on Facebook, doing what looks to be some very fine work. His page is called Beauregard's Tailor. His prices for RD I, II and III are priced about 15% lower than Chris's stuff. The two or three pieces I have seen first hand are quality items.
Bringing the