Some large Items might be good second hand, but your average, 20ft pole will be on the verge of there clamps spinning, controllers less than half life gone, pumps the same, hosereels about to fall apart and hose ready to burst.
Why take the risk when the sellers want 70% of the new prices.
A little used 60ft pole is a different matter unless its over 5 - 6 years old with old style clamps and you have thouroughly examined first,, tanks may be a safe bet, as its hard for anything to go wrong with them..
I once bought a second hand static ionics system, served its purpose but after further research I could have had a brand new Purefreedon for the same price.
Its horses for courses, but new stuff is relatively cheap compared to second hand, why take the risk
Do you want to spend all your time fixing equipment, or spend that time cleaning windows.