If something goes wrong, guides can cancel a transaction and issue a refund.
You can issue a full refund to the guest from your PayPal account. Follow these directions.
PayPal will refund the percentage portion of their fees for both transactions, but not the fixed fees. This means that for each refund the guide will lose the fixed fee (which is $0.30 in the US, £0.20 in the UK, etc - you can see the fixed fee of your country here).
Then contact Nonlocal and we will refund to you the transaction fee for that transaction.
When users use Nonlocal they are automatically covered by PayPal's Buyer and Seller Protection Program in case something goes wrong.