Most definitely!  I would advise only purchasing second hand testers from reputable companies and you should make sure it will come with a current calibration certificate or better still that the supplier has it calibrated before you buy it.  I personally would never buy a second hand tester off a private individual via e-bay; I know of one person who did and regretted it.  In good faith he purchased a Seaward PAT 1000S machine and when it arrived it was the American version (120 Volt 60 Hz instead of 240 Volt 50 Hz and set to American pass/fail limits; not UK) and totally useless in this country.