I suspect that MD has plenty of regulatory hoops you’re supposed to jump through. Just a guess on my part.
Yep:
From the article linked above:
Private gun sales are permitted in Maryland, but with important requirements. All private transfers must go through a licensed FFL dealer for a full background check. Direct person-to-person transfers without a dealer are not legal in Maryland. See Md. Code, Pub. Safety § 5-101 et seq.; Md. Code, Crim. Law § 4-301 et seq..
Additionally, if the firearm was left in the control of someone other than the original, registered owner without a background check and documentation by a ffl, that may have been a violation of MD law as well. I’d give careful consideration to whether l want to get involved with this deal. YMMV.