PayPal can now do the pre-authorization thing under their Adaptive Payments API (see https://www.x.com/docs/DOC-1419 https://www.x.com/docs/DOC-1419). We did e

PayPal can now do the pre-authorization thing under their Adaptive Payments API (see https://www.x.com/docs/DOC-1419 https://www.x.com/docs/DOC-1419). We did exactly what you're talking about (one-time preapproval, and then either charge or cancel after a few days) for a project earlier this year. You do have to explicitly apply to PayPal for access to these advanced APIs, but we found that process to be quick and painless. The API is relatively clean. When we were working with it earlier this year, the end user had to have a PayPal account, which might be a barrier. However, my understanding is that this is no longer required (https://www.thepaypalblog.com/2010/06/it%E2%80%99s-official-guest-payments-is-now-live/ https://www.thepaypalblog.com/2010/06/it%E2%80%99s-official-...).