Uncommon Apps should create and maintain a pdf document with fair, useful information about competing podcast apps that do not use the subscription business model.
When someone complains to Uncommon Apps about the subscription model, if Uncommon Apps cannot change the person's mind (which will be the usual case), then Uncommon Apps can offer to forward a list of alternatives.
This would allow Castro support tickets to end with something useful. Uncommon Apps is losing this sale regardless, but at least there is some reputational gain.
If that wasn't the root cause of his/her rage, it might be that the person felt the referral was a way to get rid of them, rather than a way to help them.
It's tricky because communication involves so many soft factors.
Quite the opposite. If somebody has a bad first impression, they will not bother contacting a business. They'll find an alternative.
If I contact a company to decide if I want to become their customer, I probably like them.
If I contact a company about a post-sales problem or for technical support, it's a different story.
Then that's not your first impression.