From various European suppliers from which I got my scanned (for most of the games) cd-keys. I trust them, they trust me. They sell more than 200-300x scans per month.
Trust me, you
can't get a legit (non-cracked, non-stolen, non-phished, non-carded, non-...) code for a price ranged between $4-$7. Same with steam accs. You can't get an account between $5-$30 with many games (acc costs between $100-$2000 - all games purchased one by one from the original owner) without any PoPs (Proofs of Purchase - scanned cd-keys of the activated games, receipts from the credit/debit card or PayPal/Moneybookers/WebMoney/PSC receipts and/or a Steam Support Account). This means that account that is selling to you is
stolen/phished and that's why is for sell for such a super low price (on the
BlackMarket!). And in most of the times buyers know that but but they still wants to "be scammed" buying them. Alright, no problems, but the risk is the account to be retrieved/recovered (from the original owner), so they choose (most of the times - yeah, big lose of money

). For low digit accs or accs with games like CS/HL/etc., risk is 10-20% only (but still there
IS!).
I'm not from yesterday in this "business".