So I have had my eyes on some new coilovers, well maybe a used set as well but I dont know how to tell if the strut is good or not?

Is there anyway to tell if they are off the car?

 

It's pretty hard to tell when it's off the car but my guess would be to look for any leaks.

If you can get it on the car, then look for sagging, any kind of rattling, it may bottom out, stray to the side under hard braking.

If the coilovers are of a good brand and don't have a ridiculous amount of miles on them, I would say they're good to go unless they've been terribly abused.

 

Leaking - Reach in, grab the strut and pull sideways watching for movement and listening for a noise - car bouncing after crossing bumps.

 

does the car bounce alot? or if the struts are leaking

 

My front right made a pretty bad knocking sound when I went over small bumps. The bouncing was only noticeable over quick bumps. You could also see residue on the strut body at the base of the spring. I sent them back to Bisltein to have them rebuilt. The knocking is gone and the car handles great. No issues thus far.