I wouldn't quite say guaranteed. Just search online for Amazon holding funds and you will see lots of people's funds are tied back for a long period of time. But 95% of the time you will get your money after that initial waiting period. Note: waiting period only starts after you have sold first item (and i think that's after you "confirm" shipment). If you don't confirm that shipment, that 14 days may never start counting.
Does the website take credit card? If so, you are in fact getting your free financing that way. If you have more than 1 credit card, look at the billing cycle for them all and find the one with the next billing cycle farthest from today. Be diligent in paying that balance off. If the place you are ordering from only accepts Paypal, in most cases you can pay by that via a credit card. Same deal.