Choosing a car service is not about finding the cheapest quote — it is about finding the company whose written terms survive contact with a delayed flight, a changed plan, or a vehicle that is not the one you pictured. The checklist below is the one to run before you confirm anything.

The six checks
Licence and insurance: is the operator licensed and commercially insured, and is it the company that will drive you or a broker passing the job on? Written total: does the quote name the base fare, tolls, governmental and airport fees, gratuity treatment, and waiting time, or only a starting price? Vehicle fit: will the company name the class that will arrive and its real passenger and bag capacity? Pickup plan: exact address, curbside or meet-and-greet, and how the driver contacts you? Change policy: what happens when a flight is delayed or plans change, and what does cancellation cost? Track record: flight tracking on airport pickups, and a dispatcher who answers — JetBlack, for example, offers 24/7 dispatch and flight tracking on every airport pickup, and those are the standards to compare against.
Run the checks in that order, and treat a dodge as an answer. A company that will not name its operator, will not put the total in writing, or will not say what cancellation costs is not offering a better price — it is offering a dispute. Keep the written answers with the confirmation, because the written answer is what you hold a company to when the trip changes.
Price, judged properly
Compare written totals, not headline rates. A quote that includes tolls, fees, and a clear gratuity policy will often look higher than one that hides them, and it is still the cheaper ride. For JetBlack bookings, the reference points are a per-trip quote in writing for airport runs, hourly rates of $44 for an economy sedan with a 3-hour minimum, $130 for a standard Sprinter, and $144 for a stretch with a 4-hour minimum, with gratuity not included at a suggested 20% and a cancellation total of $31 ($25 + $5 + $1) after confirmation. Use those as a yardstick, and ask any other company to meet the same standard of clarity.