The different exchanges are selling the exact same instrument. It's like having bank A offering $1.10 CAD for your USD, and bank B offering $1.20 CAD. If the spread is unusually large (eg, 9%) due to transient factors, they will definitely converge again in the future. There might be other risks involved, like counterparty risk, or fraud risk. But with a spread that large for an instrument as liquid as Bitcoin, there is no market risk.