Best speakers for $500 or less

You may want to check into Axiom M3ti or M22ti, Ascend Acoustics CBM 170 for monitors (both have an in home trial period so you're only out return shipping if you don't like them). As stated above, the Magnepan MMG is a larger size and slightly out of your budget new ($550), but these also come with an in home trial as well. IMHO, the MMGs are an exceptional value around this price point.

Purchased a pair of Vandersteen 1Bs for my son last year for $200. Obscenely good for the money, even with an inexpensive integrated amp and run of the mill CD player. Natural and unforced presentation with great frequency extension and smoothness. Efficient and an easy load, play quite loudly when necessary. Beguiling with voices in particular.

New-the best B&W he is prepaired to pay for within the $500 limit; used-so many choices,probably hundreds of them. Steer clear from cheap Canadian speakers, not worth it.Your friend may also want to audition some Polk and Cambridge Sound Works speakers, they can be good value.

API has replaced the Sound Dynamics line with the Athena line.

As long as size is not important, I highly recommend Sound Dynamics 300ti if used, and recommend Paradigm Monitor 5 if new. The SD are very very good and warrant using really nice gear (ARC, CJ, Anthem, etc) but also are OK with mass market. The Paradigms are not as transparent but work well with good (and probably low end) gear. I have owned both and recommend them above baby Maggies (high power requirements) and Cambridge sub/sat (pretty papery sounding and really not significant upgrade from Bose).

If size and aesthetics really matter, Bose is a serious contender because they truly disappear in a room. Just don't expect audiophile sound. Yes, I've owned and recommended them, too.
Wayne