That is a VERY simple and light weight enlarger. There isn't much that can go wrong with them.

I'd open the front and check to make sure a condenser lens is inside and undamaged
Also make sure, a film carrier of proper size comes with it.
Make sure the head goes up and down smoothly and locks down securely
Make sure the focus actions are smooth
Make sure the post is undamaged and does not lean one way or another (except for the front lean)
You could stick in the film carrier, turn it on and focus. Make sure the projected rectangle is reasonably accurate and sides are parallel to each other.

That's about it....