The marketplace doesnt facilitate try before you buy.
You need to set it up with a payment provider that is set up to allow authorise & capture as separate steps (TI supports Authorise.net and Stripe for this). The customer make the payment and its authorised, but not captured until you click accept.
If you decline you can either add the text to an email the customer receives, or you can set to a certain status with text associated with it and they will see that onscreen. You can also delay orders.