By Deborah Austin Prudent decisions about joining business-to-business (B2B) communities hinge on understanding who has ultimate control, says a recent bulletin from International Data Corp. (IDC), titled "Know Thy Market Maker: Picking the Right B2B Option for Your Business." Many e-marketplaces and supply chain exchanges lack promise of ongoing benefit to buyers or suppliers -- as only their largest customers and essential suppliers have a say -- says IDC. These one-sided B2B solutions do not have a bright future. Better possibilities: B2B sites that function as trading and community centers for all participating. These support order placing and taking, and provide community-building services such as collaboration with other players, information on products and markets, and small-business-friendly payment systems. IDC is a Framingham, Mass.-based IT research, forecasting, and advisory firm.