If a tax accountant or CPA doesn't tell you that all income is reportable, then s/he could be liable for falsifying tax forms.

If you don't tell them your total income, then it's on you.

Right, they have to advise of the truth and file accurate tax forms, or they get into trouble. Also correct, if you don't tell them, than they have no way of knowing and aren't responsible for our errors.

The old limit for issuing a 1099 was $600 so in reality, you had to earn $600.01 before someone paying you, had to report that money. The old limit for eBay was different than someone who hired you to do some work: at least $20,000 in gross merchandise value and exceeded 200 transactions for goods and services on eBay. Either way, that's the regulation for reporting and issuing a tax form, not the regulation for someone reporting income.

https://www.irs.gov/pub/irs-news/fs-07-23.pdf

Income resulting from auctions akin to an occasional garage or yard sale is generally
not required to be reported. However, there may be exceptions. If an online garage sale
turns into a business with recurring sales and purchasing of items for resale, it may be
considered an online auction business.

So it's not as simple as, all income must be reported, there are situations where if I was a business or a hobby, then it's supposed to be reported, but if it's just an occasional sale, it might not.

I don't see anywhere that the IRS says, that there's any low or high limit on personal or rummage sales or not business or hobby. But they do say, if it's a business or hobby, you must report all income.

I am not an accountant. I pay someone to do my taxes because she goes to classes and knows the laws. She calculates my equipment depreciation, income and expenses (and also tells me, things that I try to claim are not allowed). But I will say, after what I pay her, vs the self calculated taxes using "free" software, I always pay less. That and I haven't been audited since I started hiring a professional instead of trying to figure it out myself.

If I get paid by cash and don't tell her, it doesn't exist. If I get a check from a club to cover my expenses for showing up, lodging, food Etc. they don't report that and neither do I. It's entirely an expense compensation, not pay.