If it's a Winchester, it's military issue. Early M1 carbines had the flip type sights and newer versions had the ramp style adjustable sights. The bayonet lugs were also a newer addition.
$500. is an excellent price if it's mostly original and in good shape. What condition is it in? How's the barrel and crown, does it operate smoothly? Is the wood in good shape and are there any markings on it? Rust? Pitting?
Also check the magazine release and safety. If the safety is the push type, that is correct for an early model. The newer models had a turn or twist type of safety because too many guys were hitting the mag release rather than the safety and dropping their mags.
“If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen.” ― Samuel Adams