I would always be wary of any seller who offers express satchel post, if I need something quickly I would contact the seller first and ask if they can post the next day after payment, if they replied in a reasonable time saying yes I would probably trust them and purchase.

If they didn't post strasight away I would just open an item not received dispute and escalate to a claim, if the item arrived after the dispute was closed I would use their time management model to re make the payment;-)