As above, depends on costs. Full on correction should be around £500+ but that's probably overkill. Enhancement detail is cheaper and basically means they thorough decontaminate the car, run a machine polisher over it which will improve the paintwork and then use a wax or sealant. They should be able to do similar to the wheels, clean the door shuts, treat the plastic and rubber trim. Interior usually costs extra.
Ask what's involved. Have a look other detailing companies (on here there's Miglior, Midlands Car Care, Detail My Ride). Look at what they offer for the money. Don't be bogged down in the details of this place does 24-steps, this one does 100. Majority are the same and you can make up steps if you wanted to.
In all honesty, it's worth it IMO. It costs more to do it yourself unless you plan to invest time, energy and equipment and it is a lot easier to clean and keep clean thereafter.