Small businesses absolutely can, and should claim any valid expenses. In theory audits are not punishments. They happen to large companies too. But in practice small businesses often don’t have full time accountants keeping their records and some receipts are lost after the cost has been reported.

Like many compliance regulations bookkeeping has costs that larger business are easier able to bear. Small businesses do get some aid notably a lot of money went out during covid, but big businesses have the people and resources to take advantage of that aid more than a solo proprietor who wasn’t even aware. Although small businesses never seem to get those “to big to fail” bailouts.

To touch on the hobby point if you run a business 40 hrs a week and lose twice what you make a year the IRS probably won’t mind. But if you’ve got 3 businesses you use to right off expenses (like craft brewing equipment, leather working tools, or art supplies) and you only have ever sold a single belt on Etsy over the span of a year they’ll probably have an issue.