Complex sentence: Valve has set a 15% transaction fee on such sales, and game publishers who employ the Market add a transaction fee; for example, the first game supported at the beta phase, "Team Fortress 2" by Valve, included both fees.
Split into simpler sentences: Valve has set a 15% transaction fee on such sales, and game publishers who employ the Market add a transaction fee. For example, the first game supported at the beta phase, "Team Fortress 2", included both fees.