If you have that many questions on the subject, you might want to refer the client elsewhere.  Stick to what you do well and leave the other stuff for someone else.  It's much safer for you and the client that way.

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 As usual @BobKamman gives helpful information that will lead to a very supportive answer that will keep everyone in line with all IRS guidelines. 

https://turbotax.intuit.com/tax-tips/self-employment-taxes/a-tax-filing-factsheet-for-ebay-sellers/L...