The Beretta Silver Snipe is a very nice, well balanced, basic gun. They typically have a single non-selective trigger, fixed chokes and extractors (vs. ejectors). Some early ones did not have a vent rib, but later ones it was standard. The earliest guns also had an octagonal monoblock vs. the rounded one we are used to seeing. They also tend to be on the lighter side and make a great field gun.
If you like the feel of the gun and can live without screw-in chokes, a selective trigger and ejectors, I highly recommend these guns. Depending on condition, $499 is not a great deal, but people are bird hunting right now, so it probably won't last too long at that price. I'd be happy is I could get it out the door at that price if in excellent condition, $450 if more beat up.
I have a 20ga version of the gun and it's a great upland shooter. If I was a 20ga guy, this gun would be my regular shooter, but I actually prefer to carry my 12ga in the field.
An alternative to this gun with be the 686 Essential or Silver Essential that came out 5-10 years ago and are now in the $700-800 price range. These guns come with selective triggers, ejectors and screw-in chokes, but they tend to be a little heavier than the Silver Snipes. As mentioned above, the Ithaca SKB 500 20ga O/U is an excellent gun for the money, but the 12 ga guns tend to run a little too heavy for me.
Happy Hunting