what it are you after? cold side fermenting equipment is best bought new as unless your investing in Stainless Steel the usual plastic is susceptible to scratches n scrapes which can harbour unwanted microlife and protect it from cleaning and sanitation rituals.
if your looking into ag brewing and are at all diy inclined with the skills to wire a plug, drill a hole and tighten a nut, your probably better off doing a diy build. you can find all the support info needed and get help if stuck in here..
If buying 2nd hand look through the classifieds on sites like this and Jims etc first before hitting ebay, IMHO folk who post regularly in forums will value their online reputation above a little profit achieved by passing on infected equipment..
but still imho buy any fermenting vessels you use new.. you dont need to use specific brewing buckets, any foodsafe container of a suitable size can be employed, I use 25l jerrycans on occasion..
PS Welcome