The price changes the moment they arrive
A real locksmith gives you a written estimate over the phone, in a range that includes the service call, drilling (if needed), and any rekey. A scammer quotes "$15 to $39" to get the dispatch, then invents add-ons on the curb: "high-security lock fee," "after-hours surcharge," "drilling fee." If the price you're quoted on arrival is more than ~25% higher than the phone quote, walk away. They're banking on the fact that you won't.