While I think all of us would like to buy everything brand new, sometimes it is either not in our personal budgets or you just don't want to spend the cash or have the payments for new.
Buying used appliances is much like buying new - do your research! If you have the time to shop a bit, find out what is the most dependable, easy to maintain, older appliances out there. Check your usual sources; online, friends and relatives, and your friendly appliance repair tech. If you have to get a used appliance in a hurry (personal experience: power outage killed the compressor in my refrigerator and it was too old to fix and on a weekend to boot - luckily I know people!) I would steer clear of want ads.
Why? Sometimes, and I've heard horror stories here at work, people lie. I know, hard to believe, but that little whine in that front load washer you just picked up for $100 is actually the rear bearing going out and it's going to cost you about 10 times that to fix - that's why the previous owner was getting rid of it. Yeah, it works great now but not for much longer! It is a definite buyer beware situation!
I would contact either your appliance tech and see if they sell reconditioned appliances, or find out a company that does. A lot of times people upgrade their appliances or remodel, and their old appliances are fine but don't fit into the new spaces or decor, so they have to get rid of them. Sometimes they will sell them in the want ads, but also they may call someone to haul them away. Oft times, the company selling them the new appliances will install the new and haul away the old. They then will either refurbish and resell themselves or auction/sell them to others who do the refurbishing.
These companies will go over these used appliances and determine whether they are worth refurbishing or destined to the scrap yard. They will clean them inside and out and replace parts (belts, rollers, seals, refrigerator door bars and end caps, drawers, hoses, etc.) and make sure the appliance is in good working condition before they let it out the door. They will even often some sort of warranty on it.
So, if you are looking for a second refrigerator for the garage, or on a tight budget, be as careful at buying a used appliance as you would buying a used car.
Have a great week!