How can I confirm if a composer is a specified service business or not?

[OH EA]

Is there a resource to classify a profession as specified service or not?

[G4Trax]

Review https://www.irs.gov/newsroom/tax-cuts-and-jobs-act-provision-11011-section-199a-qualified-business-i... and possibly take some CE on 199A 

[Stephen L Nelson CPA]

I think you read the final regs discussion of the performing artist category... and then you carefully question your client as to whether he or she spends more than ten percent or more of their time doing performing arts stuff.

Note: The regulations talk about a writer "paid for written material, such as a song or screenplay, that is integral to the creation of the performing arts" ...counting that as a performing arts SSTB (page 83/84 of final regs)... and then other writing as not qualifiying.

BTW, I think the Section 199A cliff is something to watch out for too. Just a little bit too much performing artist activity (or consulting activity) will taint the entire business as a SSTB. (See Reg 1.199A-5(c)(1)...)