First of all, FYI, IRS doesn't allow losses taken against hobby income until it rises to the level of a business and is reported as such. IRS won't fix most errors that favor it with a few exceptions.
Second, IRS has no threshold or minimum for reporting any type of income per se, a taxpayer is expected to report ALL income except that is specifically exempted by law, except if the taxpayer doesn't meet the requirements to file. Regarding materiality, IRS requires payments of $600 or more to be reported on a 1099-MISC.
I would opine that if IRS was concerned about such transactions, the forum would be required to issue 1099s like barter houses do.
"Generally, an amount included in your income is taxable unless it is specifically exempted by law. Income that is taxable must be reported on your return and is subject to tax. Income that is nontaxable may have to be shown on your tax return but is not taxable. A list is available in Publication 525, Taxable and Nontaxable Income." https://www.irs.gov/businesses/small-businesses-self-employed/what-is-taxable-and-nontaxable-income.
Use your best judgement...
