I agree, probably not much past history unless Rich tagged him during the war.
Rich has very few still on his shoot on sight list, so Marcus most likely isn't on it. He's actually fairly tolerant of people's past history, but also keeps in fighting shape and usually carries two or three wands and has been known to wear a Walther PPK in a shoulder holster. Marcus might push some of Richard's paranoid buttons until they get better acquainted.