My wife has talked the kids and I out of 3 garage sales now. We just take the stuff worth selling to our local "Family Services" outfit who run a resale shop and provide goods to the poor.
They give us a little "tax form" and we write off the goods at about what we would have sold them for at the garage sale. Already done it twice, once in Aug and once in Sep. The trick is to remember to keep the form for tax season, so file it away. Given that we had a bad tax year last year (kids are finally too old to be able to deduct day care), we're trying everything we can to save on taxes.
We volunteer there occasionally, as well. You would be amazed at the "working" stuff I've found. One guy walked out of the store with a working LaserJet series printer (printed a test page anyway) for $10. I work with them to determine if the computers and monitors are working when I'm there.
Books are very cheap as well. It's kind of like Forest Gump's life, you never know what you're gonna get. But, you always know what you're gonna give.
Glen