Last week I bought a 2013 Mustang premium with 44k on the odometer... I know that the car was an AVIS rental prior to my owning it.
Smoke smell should eventually go away...hopefully. I would be more worried about it being an AVIS rental car. Rental cars, especially Mustangs, get seriously beat on...at least in MY experience.
2013 Mustang GT Premium (6 speed manual, 3.73 gears, GT500 axle-backs, no resonators), 1998 Pontiac Firebird Convertible, 2003 Jeep Grand Cherokee, 2007 Honda ST1300, 2001 Ninja 250