Is $500 for a Nikon D90 dslr body a good deal?

Is it a good deal for a beginner? It's used, but looks good and well taken care of. Comes with box and manuals. Does NOT come with lens
Is there a maximum actuation count it should not exceed for that price?

If it is pre-owned then I suppose it would be a good price. BUT if you live in Australia (not sure if you do) then you can buy a brand new one (i'm 99% sure its brand new) from this website. It also comes with "a free gift," though i'm not sure what it is… The price on this site is $499 AUD. Hope i helped! XD

http://www.techrific.com.au/nikon-d90-digital-slr-camera-body-only-premium-package-free-shipping-both-ways-p-1250.html

Well, it was a superb camera in its day and is still a good camera, but it's getting very dated by today's standards. By the time you throw in a lens, you're looking at enough money that you could buy a new D5100. Not a "pro" camera like the D90, but things have come a long way in the 6 or more years since the D90 came out, just like computers have. And look how outdated a 6 year old computer is.