I will say I do trade by Beckett value.
Only 1 card in my collection was bought for BV (everything else bought for under on Ebay) and that was a card I told my dad I really wanted and he bought it for me because I'm constantly trading for cards he needs. It was a 91-92 OPC Premier Vladimir Konstantinov RC ERR. Once it's into the trading arena I go mostly by BV with a mix of my own ideas and projections.