Agreed. It doesn't take a lot of working with PayPal to know the IPN system is fragile at best.

PaymentDetails is mandatory for any adaptive payments integration.

https://developer.paypal.com/docs/classic/api/adaptive-payme...

That's very close to what I've always done. I have a notification to warn me if I have new failed sign-ups due to payment and keep Paypal responses to catch all sorts of problems. It's just good practice to expect things to fail sometimes. That's also why I have my status page hosted with a different provider and twitter status as a back-up for that.

My favorite Paypal annoyance is that for split payments there's no way to verify that a seller's Paypal account qualifies for split payments (has to be a business account and verified), without trying to send a payment. At least, that's the way it was last it mattered to me.

Actually you can check if an account is verified!

Here's a snippet in Ruby I use to check. It's not perfect, but it catches a lot of cases:

    # ...

    def initialize
      @request = PaypalAdaptive::Request.new
    end
    
    # ...

    def verified_status( opts={} )
      begin
        opts.assert_keys! :first_name, :last_name, :paypal_account_email
        result = @request.get_verified_status(
          emailAddress: opts[:paypal_account_email],
          firstName: opts[:first_name],
          lastName: opts[:last_name],
          matchCriteria: 'NAME'
        )
        Rails.logger.debug "PAYPAL VERIFICATION: #{result.inspect}"
        return result.success? && result['accountStatus'] == 'VERIFIED'
      rescue
        return false
      end
    end

Here's the API docs: https://developer.paypal.com/docs/classic/api/adaptive-accou...

What I can't stand is that accounts in some countries (at least India) can't send payments from balance. So you can't get your fee. This is mentioned nowhere in the docs, a customer just hit it one day and that's how I found out. I asked paypal what other countries can't send payments and they said... wait for it... they "don't have a list". I kid you not: https://twitter.com/rfunduk/status/412980259001102336

Belt and suspenders, dude, belt and suspenders.

When dealing with PayPal, go for an elastic waistband as well :)

Agreed - the statement of "Because of how critical IPNs are to any Paypal integration, we didn't think to double check if IPNs were not being sent." is exactly why you should double check - anything that is critical needs tests and backup solutions.