How about looking at purchasing a machine from a different angle? Years ago I worked for a sewing machine retail store. We used to take in perfectly good machines turned in for an upgrade type of machine. While there may be lemons out there, I think you'll be OK buying used if you take the time to work with a reputable dealer. That person will know what they have available for purchase and should be able to provide a couple of classes to show you how to operate the machine.
But hold on ... there's another reason to consider buying a used machine from a dealer. They should do a check-up on the machine before selling it to you (clean, oil, test stitching, etc.). If you have problems trying to do something, they're usually willing to help you out. Do you get that at Wal-Mart? Please understand I'm not bashing Wal-Mart. I shop there. I do have a name of a dealer in Michigan who I would highly recommend to anyone but I don't think you're in Michigan. I've purchased 3 machines from them. They currently are selling Brother, Pfaff and something else (can't remember). The good thing about them is that they also used to sell Bernina (among others)and have all those parts accessible if needed. The owner and his staff are all very knowledgeable in almost every machine on the market today so they have a wealth of information for you if you take the time to do some research.
One of the key things I always consider buying a machine is where I'll have to go if I have problems with the machine. Where would I have to go to get it fixed if the timing goes out? Machines do that regardless of the make, model, or cost. I've had machines through the years that were anywhere from $100 to $15,000. They all need tweeking once and a while. I once purchased a machine for about $200 that had retailed for about $500-$600 just a couple of years before. The previous owner was someone who always liked to have the latest and greatest of everything so never really put much sewing time on any machine she ever owned. I got a great machine which had been used long enough to know that all the "kinks" were found but still had a really great machine (no scratches or dings at all) for a lot less money. It's been a great machine.
People buy machines for many different reasons. Each one is looking for something that's important to them. One may want to be able to hem jeans while the next person wants to make delicate lingerie. Unless you are able to actually spend some time sewing on the machine you're considering you won't know if it's a good match for you or not.
My final thought for any one considering purchasing a machine ... take some time to do your reseach before you make your final decision. Don't let cost alone be you're deciding factor.