See below for the details about each of these payment methods. You can specify the mod for bitcoins addresses of sellers in the configuration file, or use the email addresses registered for each user.
Coinapult say they will return money to the payer if it is still uncollected after 30 days. In future it should be possible to build this functionality into the OpenSim viewer, making the experience more seamless. You will need to sign up for an API key with them and add it to your configuration.
If it somehow produced incorrect information, you could end up selling things for the wrong prices. This may also require you to change your pricing, if you have priced in Bitcoins rather using a traditional currency and letting the system convert it.
Metrics details Bitcoin is strikingly beautiful in its abstract cryptographic design but a nightmare on earth regarding concrete environmental realities. It is also a symptom of a sci-fi libertarian tendency to find clever technological solutions to problems that we do not need to have.
This should be fine for most practical purposes, but in theory it is possible to double-spend money at this point, with the result that the payee never receives it. This can be avoided by checking how far the payment has been confirmed by the network, but this will cause payments to take longer to process.
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To be absolutely certain of payment, you need to set to 6 confirmations, which takes an average of 1 hour. See the comments in the freemoney.