Unless you use escrow (which involves trusting a third party) the buyer risks a no delivery of goods and/or services with no recourse. Check out the scammer accusation subforum.
No chargebacks is an inherent feature of bitcoin. It doesn't really increase risk though, it just MOVES risk from the receiver to the sender. The flip side is that it's much safer to GET money with bitcoin. In any case I suspect escrow services will become standardized with time.