We charge for briefing time in a reasonable non-rip-off way. If unable to fly because of weather, students are offered ground briefing and pay a nominal amount (eg I may spend two hours doing a long nav brief and then they buy me coffee/sandwich and get charged an hour's ground instruction). It's up to them if they prefer to go off on their own and read the book though most take up the offer of instructor time.
To put it in context, I'd charge for briefing a full aircraft check or a session on airlaw - but not for a regular pre-flight brief.
Our students seem perfectly happy with this. They say they get very good value. Often, two of them will sit in together and split the cost.
Aren't there any other schools that work like this ?