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I'd like to build a web service similar to kickstarter that allows users to pledge money to an idea, tho I'm unsure how I can implement this kind of payment system. If the the idea receives a specified amount of money, then the donors are charged. If it doesn't, the donors are not charged. I've done some preliminary research and have found Amazon Payments to be a possible solution provider for this, but I'm still unsure where to start with this and was hoping someone could point me in some right directions for how I can go about implementing this kind of payment structure in my web site.

I should also note that this is primarily a prototype I'm building, so it's ok if the solution is limited to U.S. customers only. Also, I plan to build the site using Ruby on Rails.

Thanks so much for your wisdom!

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closed as too broad by MetaFight, Scant Roger, Ixrec, Bart van Ingen Schenau, gnat Jan 4 at 21:33

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Are you sure you should be building that service? There are existing services that do that, and it's usually best to be conservative when handling other people's money. – David Thornley Feb 28 '11 at 16:15

This process is known as authorization & capture and is used by most major payment gateways, including PayPal and Amazon (Amazon refer to it as delayed order fulfillment or Reserve action).

PayPal on authorization and capture

Amazon on the Reserve action in their API

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Thanks, Eran, I was just reading about PayPal's approach when I saw your response :) – BeachRunnerJoe Feb 24 '11 at 22:16

You can also use an online escrow site (which might be more appropriate for you).

Warning - if you do use an escrow or payment site, only ever use a Government registered site (there are unregistered scam escrow and payment sites out there).

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