Do your home work. Check your items out on ligitimate sites like
audiogon or ebay for guide lines on prices. Check out equipment
reviews on audio review.com.
Make sure your person you deal with has some sort of verifiable
account such as paypal ect with references ect. Blue book values have
nothing to do with sound quality there for are of no value. Again
check ligitamte sites on equipment reviews. There are alot of stupid
people out there. Ive done 120 large transactions totalling about
75,000$ with not one problem and have always made money on everything
i buy always buy with the intent to resell for proffit. If you can not
make say 10% on the deal forget about it. Make a understanding with
the seller that the equipment must work for a period of time after the
sale or help with repair cost. This will help.