IME, I dont think it's so much as Avis, but moreso the DC area. Anytime I've rented from Avis/Hertz out of DCA or IAD, I usually always get a car that is in a lot worse shape than it should be. I've also gotten cars with 50-60k+ miles on them out of those airports as well. I find BWI to be better with keeping their cars maintained, have a stocked Preferred Select & Go section, etc.

Now that I'm PC, I've gotten basically new cars (3 times < 1k miles) and once a Fusion with 4k miles. This has been all out of SEA though during normal business travel times (M-Th).