TurboTax
at https://ttlc.intuit.com/questions/1901108 explains ItsDeductible values as follows:
How do you determine the
fair market value?
To determine fair market values, we gather
pricing information from auction websites like eBay as well as resale outlets
and thrift stores across the U.S.
Every day we collect information from
hundreds of thousands of completed eBay auctions to capture valuations that are
not commonly found in thrift, consignment, or specialty stores.
We then perform a statistical calculation to
determine the fair market value of the item, which is then translated to a
high, medium, or low value.
We also collect pricing information through
manual processes, for example surveying thrift and consignment stores across
the country.
This combination of electronic and manual
price-collection allows us to create a comprehensive, up-to-date collection of
values based on real-world transactions that comply with IRS guidelines.
