Who in the U.S. would be able to appraise donations of over $5000 in regular clothing for tax purposes?

Don't know, but based on the value of "used clothing" you'd have to be donating an awful lot of clothing to have that much, either that or donating mink coats, and expensive dresses or suits. You don't get anywhere near original value of the clothing. I think if you tried taking that much of a donation for clothing you're just inviting an audit by the IRS.