When you buy or sell on an exchange, you're not transacting against the exchange, but against a counterparty, via the exchange; someone like you, but making the

When you buy or sell on an exchange, you're not transacting against the exchange, but against a counterparty, via the exchange; someone like you, but making the opposite transaction. If you sell a Bitcoin for $10k, then someone else brought $10k to the exchange and offered to exchange it for a Bitcoin. The only way an exchange wouldn't be able to honour deposits is if they lost them, or because of fraud. A surge in price shouldn't affect the solvency of the exchange.