Picked up this awesome Biosonics 8-piece tuning forks set at an estate sale for a cool $5 and it sells for ~$200 on eBay! This item was NOT PRICED at the sale, but it caught my eye so I used my phone to IDENTIFY the item and also to look up SOLD PRICES on eBay. I then took it to their checkout and they offered it to me for JUST $5!
Always remember that the companies that run estate sales want to SELL THE STUFF. They know that they can't look up every single item and that they can't get "eBay prices" for everything during their one- or two-day sales.
So when you find things that aren't priced at estate sales, look them up and then ask for a price; you might be pleasantly surprised!