The most expensive reports are the ones that look finished. A default GA4 property will happily produce clean charts built on events nobody defined against revenue, and a business will set budget by them for years.
Form loads are not conversions
If your conversion event fires when a form is displayed, or when a thank-you page loads that anyone can reach, your conversion count is fiction. Tie the event to the moment the business actually gains something: a qualified enquiry, a booking, a payment.
Last click flatters the wrong channel
Branded search will always look like your best performer under last-click, because it's the final step of demand something else created. That's not a reason to abandon attribution — it's a reason to read it alongside spend changes over time.
One view, not fourteen
Every measurement project should end with a single view you'd be comfortable making a budget decision from. If a dashboard has never changed a decision, it isn't reporting — it's decoration.