This note contains considerations on the existence and non-existence p
roblem of conformal scalar curvature equations on some complete manifo
lds. We impose two general types of conditions on complete manifolds.
The first type is in terms of bounds on curvature and injectivity radi
us. The second type is in terms of some particular structures on ends
of manifolds, for examples, manifolds with cones or cusps and conforma
lly compact manifolds. We obtain non-existence results on both types o
f conditions. Then we study in more details the existence problem on m
anifolds with cones, manifolds with cusps and conformally flat manifol
ds of bounded positive scalar curvature.