In most cases this won't be a problem at all. The beauty of a block chain is that there is a public record of every transaction. Payments can never be lost. If there is a hangup like this contact transaxe support and they will find the payment on the blockchain.
The only time this could be an issue is if the exchange rate has swung wildly in which case a refund might be issued instead.
But don't worry you're always in good shape with bitcoins there is no "check in the mail" story possible.