Part out.
No easy way to tell if coilovers, or any shocks, are still good when they aren't mounted (not so easy when they still mounted either).
Just the obvious. Make sure they aren't leaking. Look for signs they were leaking, but were cleaned up.
Look for any external damage. Like if they were in an accident. Recently there was a set of PSS on ebay, one of the rear external reservoirs was hit. So it was bent at a different angle than the other one. It pinched the tube that connects it to the shock, so it was trash. But it could have been easy to miss. No visible impact mark, etc.
Look for overall age. How weathered they are. Gives clues as to mileage. If the price is low enough that you can afford a rebuild, then wear doesn't really matter. Some models are not made to be rebuildable. Not a good idea to buy those used.
Just the obvious. Make sure they aren't leaking. Look for signs they were leaking, but were cleaned up.
Look for any external damage. Like if they were in an accident. Recently there was a set of PSS on ebay, one of the rear external reservoirs was hit. So it was bent at a different angle than the other one. It pinched the tube that connects it to the shock, so it was trash. But it could have been easy to miss. No visible impact mark, etc.
Look for overall age. How weathered they are. Gives clues as to mileage. If the price is low enough that you can afford a rebuild, then wear doesn't really matter. Some models are not made to be rebuildable. Not a good idea to buy those used.













