I know this is a long thread (48 pages!!) and it would take some time to go back to Page 1 and read all the way through.
But your question is answered in a large number of different ways throughout these pages, with numerous examples to view, and I encourage at least skimming through the whole thread.
The easy sporrans to tell are the ones with the gold oval stamp Made In Scotland Real Leather which several different makers used over a half-century period, and some still use.
Plus the fact that many cantles have Made In Scotland stamped in tiny letters on one side.
Many sporrans are stamped giving the specific maker, usually on the back of the leather body, but Nicoll Brothers stamped the sides of some of their cantles as well.
Pakistani sporrans are almost never stamped. I don't know if I've ever seen it.
But a vast number of legitimate Scottish-made sporrans have no markings whatever! Then the experienced eye comes in.
One thing to be aware of is the various styles that the Scottish makers made in the c1930-c1970 period. See anything that looks out-of-place and it's most likely modern (post-Kilt Hire) or Pakistani. You get a feel for the vintage styles, a feel that comes from looking at thousands of old sporrans and dozens of vintage catalogues.
The Pakistani makers also make close-looking copies of many legit Scottish-made sporrans, and these can sometimes be hard to tell apart from photos. Oftentimes the front of a Pakistani sporran looks legit but the back has something not-quite-right about it.
All of these things are why on Ebay you need to see the backs of the sporrans!
Here are a couple catalogues from various periods giving some impression of Scottish-made sporran styles
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