I don't hate Paypal, but I'd prefer not to implement anything again against the Paypal API. I wrote a small e-commerce engine for a friend's site a couple of y

I don't hate Paypal, but I'd prefer not to implement anything again against the Paypal API. I wrote a small e-commerce engine for a friend's site a couple of years ago, utilizing Paypal for the shopping cart & IPN to notify the site when merchandise had been purchased. There is an extreme lack of precision in the documentation for the various APIs, that made the entire process take twice as long as it should have (or was, I haven't checked back since I wrote the implementation). When I implemented the IPN receiver I tried to find out, precisely, what data would be sent, and gave up, instead running through a series of transactions to get a 90% coverage of fields for payment and refund transactions. Receiving all of the ebay transactions for the account was a surprise, but one I was somewhat prepared for. Maybe there is a flow chart of what data gets sent with what transactions, but in the time I was doing development I couldn't find one. During that time there was some sort of changeover from the existing Developer portal to x.com for some, but not all documentation. Was extremely frustrating for links to examples to break, even more so to return months later and find them still broken. But the thing that really killed the utility of Paypal for me, and possibly doomed my friend's site, was the long delay when clicking "Add to Cart", which POSTs the relevant item information to Paypal to create and/or add to an existing cart. The delay was measurable in the multi-second range, and was entirely on the Paypal side. Totally independent of browser, O/S, network (I checked). This lead to a cart abandonment rate of close to 50% (measured via Google Analytics data, amongst other means). Never any indication of errors, no messages to the merchant's paypal account indicating anything was wrong with the data being sent. Just. A. Long. Delay. If you were patient the cart would appear with the item(s) displayed. My friend ended up shuttering her business at the end of 2011, for multiple reasons, but the abandonment rate was certainly one of them. Had the business not closed I was going to try shifting to maintaining the cart on the site and doing "upload cart" to Paypal to see if that sped things up, but we never got to try it. So, lack of precision in documentation, performance, lack of diagnostic information [aside: we didn't see the performance hit using the sandbox, solely in production].