One thing you want to keep in mind when buying used Kwifish, is why are they being sold???? I know that i have sold alott of them on ebay, just for the reason that they are not fish gitters...... about 1 in 6-7 actually produce consitently. So ya go through quite a few to find the good ones.... The good ones i have, i wouldnt sell for 3 times there price...... I would never buy any used ones just for that reason.... Call me crazy, but you can tune them all ya want, It's just some are consistently better than others.... Good luck to ya.