Also, make sure you now what you're getting with the set up and the life expectancy of those items - much like a boat or used car, a used tank will be working when you buy it, but when items fail over time, the cost to replace may be more than what it would have cost to buy knew as a package.
Sometimes, knowing what you have new is better than not knowing and finding out the hard way. Only way to avoid this it to learn as much about systems and their ways of working before hand so that if you buy used, you'll know what to expect over time and where you're liabilities may be.
Good luck with your purchase and welcome to MR
House