Expect to see your brake/oil/air filter life cut in half. most of this is due to idling in a fleet-like manner a vehicle with no accomodation for greater-than-average idle times. Example: the crown victoria and F150 fleets sold to government agencies can easily sustain a 3-6 hour idle as theyre equipped with an enlarged intercooler so you dont cook the oil.
Suspension suffers but not appreciably as power steering fluid, which turns to laffy taffy pretty reliably in these types of vehicles. Tire life in some cases is notably shorter due to the prevalence of sidewall damage from mediocre drivers dragging or hopping curbs. Fleet vehicles are equipped with idler/pitman assemblies which, again, are cheaper to repair and service than the more complex and expensive rack-and-pinion...which also isnt as durable for fleetlike operations.
service times are also longer...so theres lost revenue. example: an AC service on a Lexus takes damned near 4 hours (I'd want the car for the day.) Service on a lincoln towncar? I might not even have to put the keys in the ignition. Theres actually a factory tool you can order from Mexico that will do it in about 11 minutes.
TL;DR: if you're driving for one of these taxi services, buy a fleet vehicle used or new.