how to tell if shock is bad

i just bought some used up country zj springs for my cherokee for 20 bucks. i think one of the shocks is bad because when i press down on it is bouncey and is sort of hard to press down. the other threee simply compress down and come back up all about the same way. is my assumption correct? also i have a 3" lift, if i use these good shocks and leave one of the stock shocks is that ok until i get another shock? thanks

The one that acts diffrent is probably bad. If you run with a bad/incorrect shock it could cause premature sag of you springs.