I realize this is a very old thread but if you are still looking this is a great way to get gym equipment. If you were buying a treadmill or anything electronics or with motors I would hesitate because they may need calibration, repairs and they can wear out. At the other end of the continuum is weights (barbells, dumbbells, plates, etc...) - what can go wrong with that if they are in good shape (no rust, not bent, not lose, etc...). A 45 lb plate is a 45 plate new or used so why spend more for new. I go on Craigslist and look for local equipment and buy it that way. For all of the things I have purchased it seems I always run into one of three types of sellers (and they are all good).
The first one is a gym, health club, martial arts place that is going out of business or upgrading equipment. There was even an apartment building near my home that built a gym for the tenants and since nobody used it they sold off their stuff.
The second type, along similar lines, there are brokers that buy these items from these place and then resell them. I wanted a spincycle (not a Peloton or anything fancy) and if new, the model that I wanted was close to $1,800. I saw an ad on Craigslist for someone selling it for $250. He even offered me a $50 discount if I went and picked it up instead of him dropping it off. When I went to pick it up it was a GIANT warehouse that had hundreds of these along with hundreds of treadmills, benches, ellipticals, etc.... He had to have millions of pounds in plates and dumbbells. He told me that he buys out the equipment from gyms that are going out of business. The spincycle I bought still had the plastic wrapping on it. He told me that this gym closed down before it even opened and all of the equipment from that gym was new.
The third type of person I ran into was people who bought equipment for a home gym and decided it was not for them. I have experience on both sides of this transaction. The spincycle I bought, I only used 2 or 3 times before realizing that I would rather bike outside or throw my road bike on a trainer. Someone bought it from me within 24 hours of me posting it. I also bought a brand new treadmill form the manufacturer and had it delivered and setup. I ran on it twice. I would rather run outside and if I wanted to run on a treadmill I will use the one in the gym (there is something about the gym atmosphere that makes running on a treadmill not as boring as doing that at home). Someone got that treadmill from me at 50% of the price I paid and it was only 2-3 weeks old and used only twice.
Good luck.