See this Journal of Accountancy article on the 9 factors used to determine business versus hobby.  https://www.journalofaccountancy.com/issues/2013/oct/20138370.html

The reality is, some of these factors are not easily answered as they are "esoteric" in nature.  So the tax preparer has to take a position and present it to the client.  If I honestly believe it's a hobby and the taxpayer says otherwise, I will unfortunately have to terminate the client.  They will then easily find someone else who will take their position and argue we're idiots.

But if I feel the client has a "good leg to stand on" under audit, I will side with the client, but I will document my concerns about this (or any other issue) and give a copy to the client.  It's not like this situation is a 1 + 1 = 3.  Yes it does or no it doesn't