the short answer
Facebook ads work for personal trainers when three things are true, in this order. First, you already have an offer that converts warm leads - a clear who, a clear result, a next step. Second, you can commit a floor of roughly EUR 300 to 500 a month for four to six weeks, because below that Meta cannot gather enough data to optimise. Third, you follow up fast. Plan for a lead-form lead to cost around EUR 3 to 15, and a booked consult or application to cost more, often EUR 15 to 40 plus, varying a lot by market and offer. If your offer is fuzzy or your follow-up is slow, ads only lose money faster - post organically and prove it first.