1. Single-needle stitching versus double-needle stitching for dress shirts. If what I've read is correct, the easy way to tell is to examine the side seam of the shirt. Double-stitched will have two parallel stitches running on the outside whereas single-stitched will have one stitch and a fold with the other stitch on the inside of the shirt. Is that accurate? Do manufacturers stitch different parts of the shirt together differently?
Be sure to examine both sides of the seams. On a single-needle seam, one side should have two rows of parallel stitching, while on the other side there should be only one row of stitching. Most shirtmakers put the side with only one row of stitching on the outside, and the parallel rows on the "inside" area of the seam, but Marol is an exception. Marol sews single-needle seams, but the parallel rows are on the outside while the single row is on the inside. On double-needle seams both the inside and the outside will have two parallel rows of stitching. Mr. Kabbaz's informational pages: http://www.customshirt1.com/StyleForum_AskAndy01.htm http://www.customshirt1.com/StyleForum_AskAndy02.htm
Ike Behar's shirtmaking procedures: http://ikebehar.com/Factory/stepstomakeshirt.htm
2. How do I tell a fused suit jacket/blazer/sportcoat from a canvas (hand-made)? Can you tell just by looking?
All you really need to do is turn over the lapel and look at the underside. If the canvas has been attached by pad stitching you will likely see some "depressions." Keep in mind, though, that the lapels are not the only canvassed area of a suit. The chest is also canvassed. Just closely examine the garment.
3. Does anyone have recommendations for getting a suit custom made by a tailor that offers that service? In particular, I'm wondering if there are particular questions I need to ask like where they get their materials from and who actually does the work?
There are quite a few options. There are tailors, some who do all the work on the premises, some who send the order to a factory to make the garment. Then there are MTM(made to measure) programs of companies such as Oxxford, Brioni, Kiton, etc. For suit fabrics, traditionally the best come from the United Kingdom(esp. Huddersfield/West Yorkshire) and Italy(esp. Biella). Alias mentioned that Cheil(a division of Samsung) is weaving superfine wool in Korea.