Who operates delivery flights for commercial airlines?
When I worked for Boeing as an intern in 2000, I got to see Boeing’s wide body delivery center in Everett, WA.  Back in those days at least, the airlines brought out a crew of lawyers, aircraft brokers and test pilots.   Typically what happened was the airline’s test pilots would take the new aircraft up for a check flight with Boeing’s factory test pilots.  This consisted of flying the aircraft from KPAE east to Moses Lake (KMWH) where they would shoot a couple of approaches and test the avionics and systems on the new airplane, then fly west out past KPAE over international waters where they, at least technically, “bought” the airplane.  Doing this outside the boundaries of the US allows the airlines to avoid paying 8% Washington State sales tax on a $200 million airplane.  The test flight concluded, they returned and landed at KPAE.  After that the airline’s lawyers and broker met with Boeing’s lawyers and a purchase price was agreed upon.  A phone call was made and the funds were electronically transferred from The airline’s bank accounts to an account belonging to Boeing.  After that, the airline’s test pilots flew the airplane out and put it into immediate service.  Typically if the airline had scheduled service from KSEA the airplane was flown on a short VFR hop down to SeaTac and parked at a gate, where it was immediately prepped and began passenger service.  When I was there, Aeroflot took delivery of a 777 which was flying from Seattle to Moscow the very night the airline took delivery.  Other strange things are negotiated in the purchases.  Cathay Pacific once made a deal with a WA state cherry co op along with the purchase of an 747-400F; the airplane flew back to China brand new with 20,000 lbs of bing cherries aboard!