re: amateurs and professionals, it appears that before c. 1918 shooters could "self-declare", while still representing gun or powder makers
At the 1901 (2nd) Interstate Grand American Handicap at Targets manufacturers agents and paid representatives were permitted to shoot “for targets only” in all events but could compete for the purse in the Preliminary, Grand American, and Consolation Handicaps.
The 1905 GAH appears to be the first time separate Professional Championships were listed
https://digital.la84.org/digital/col...oll17/id/37132
December 16, 1911
Sporting Life changes for 1912
https://digital.la84.org/digital/col...d/27288/rec/24
https://digital.la84.org/digital/col...d/27291/rec/24
At the 1914 GAH, Professionals were prohibited from participating in the main event
https://books.google.com/books?id=yB...J&pg=PA771&lpg
https://digital.la84.org/digital/col...oll17/id/56949
From The Interstate Association rule book in “Trapshooting - The Patriotic Sport” regarding the c. 1916 rule.
The following rules defining an amateur and professional in trapshooting, prepared several years ago by the tournament committee of the Interstate Association, were adopted:
Amateur - Any shooter not dependent upon his skill as a trap shot as a means of livelihood, either directly or indirectly, or in part or whole, including employees or manufacturers of, or dealers in, firearms, ammunition, powder, traps, targets and other trapshooting accessories, and who does not receive any compensation or concession, monetary or otherwise, or allowance for expenses or trapshooting supplies from such manufacturers or dealers, shall be classed as an amateur.
Professional - Any shooter, including employees or manufacturers of, or dealers in, firearms, ammunition, powder, targets, traps and other trapshooting accessories, who receives his salary or any portion of his salary, or any expenses of any kind for use in trapshooting, or rebate on the market price of such articles, as compensation for the promotion of the sale or advertisement of any such products handled by such manufacturers, shall be classed as a professional.