The way I see things, a pay-per-minute phone consultation ought to involve no sales pitch whatsoever. Nobody wants to pay for that, and nobody should.

Consulting and sales are utterly different roles. Mutually exclusive, in fact.

Is your value proposition external to the call or internal? A consulting call ought to be self-contained. By the time a client hangs up, they ought to be in a better position than where they started – with no further obligation to pay us.

So ask yourself what the purpose of the phone call is. If your goal is to sell a product or service – a useful WordPress plugin in this case – then the call is a sales presentation not a consultation, and it ought to be free.

The hard truth of sales is that a large percentage of prospects (the majority, usually) won't buy, even after a 30-minute presentation about the virtues of your offering. Time spent talking to dead ends must be factored in to your price and recouped by successful sales. Adding that cost as a fee for the sales pitch itself won't work out well.

This is sometimes a tough distinction to make.

In my own case, I offer a number of services (e.g. brand name creation) that go beyond the scope of a 15-minute phone call. When someone is paying me $5 per minute, I don't want to squander their time and money by explaining some other paid service!

So the rule I've set myself is to stick to problems I can solve on the phone. When it's appropriate to explain the broader services that I offer, I try to do so in a non-paying context. Mainly through email.

There's nothing wrong with using a free Clarity.fm call for a sales pitch. But it does sound like you're using phone calls in order to pitch a purchase; so charging for such calls would probably backfire.