I would really consider going new with those. By the time you bought a set of used ones, paid to ship them to Chuck to get checked out/cleaned for another $87 (and hope they're all good) and got them back.... You'd probably not have saved much money but spent a bunch of time and shipping for a risk.
Chips on the other hand are a safe bet. It's rare they don't work, and if they're fried it's much better than your car won't start instead of losing a cylinder.
