This is a lightly used, but tested and working Black & Decker model PHS550 electric corded reciprocating hand saw.
The blades require pressing the button on the side, hooking the hole in the blade over a stud, and then swiveling the blade up. Removal of the blades is the opposite. If you've never used one of these before, then please see videos online about loading the blades because it's easy once you know the steps, but not immediately obvious if you've never seen it done.