It's not easy, by any means, unless you're already familiar with IRC and crypto and signing messages.
But it's basically anonymous: the actual transactions happen in emails or privmesgs and so there are zero records beyond the feedback on bitcoin-otc.com (which is optional and can be meaningless†, for example, the ratings by 'newguy' and 'AVALON' on me), and there's no way to prove or disprove that a transaction happened without full access to the internals of whatever systems one side of the transaction is on. For example, there's no way for anyone to prove that I really did sell 0.25btc for $50 on Amazon; there's plenty of 0.25btc movements on the blockchain, and all Amazon sees is that I redeemed a giftcode from somewhere. And there's even less evidence if you're willing to send or receive cash in an envelope (http://bitcoin-otc.com/vieworderbook.php?type=&nick=&thing=&...). So it's about as anonymous as you want it to be.
†Specifically, you can be fairly sure the AVALON/newguy accounts did leave that feedback on me because the site accepts commands only from IRC accounts which have cryptographically proven their ownership of the account; but there is no way to be sure that I transacted with them or scammed them. As it happens, I did not and those ratings are revenge from a scammer for not falling for his tricks. Same problem as with public keys, and why people talk about web of trusts.
It's not easy, by any means, unless you're already familiar with IRC and crypto and signing messages.
But it's basically anonymous: the actual transactions happen in emails or privmesgs and so there are zero records beyond the feedback on bitcoin-otc.com (which is optional and can be meaningless†, for example, the ratings by 'newguy' and 'AVALON' on me), and there's no way to prove or disprove that a transaction happened without full access to the internals of whatever systems one side of the transaction is on. For example, there's no way for anyone to prove that I really did sell 0.25btc for $50 on Amazon; there's plenty of 0.25btc movements on the blockchain, and all Amazon sees is that I redeemed a giftcode from somewhere. And there's even less evidence if you're willing to send or receive cash in an envelope (http://bitcoin-otc.com/vieworderbook.php?type=&nick=&thing=&...). So it's about as anonymous as you want it to be.
†Specifically, you can be fairly sure the AVALON/newguy accounts did leave that feedback on me because the site accepts commands only from IRC accounts which have cryptographically proven their ownership of the account; but there is no way to be sure that I transacted with them or scammed them. As it happens, I did not and those ratings are revenge from a scammer for not falling for his tricks. Same problem as with public keys, and why people talk about web of trusts.