I've bought both of our trailers from private parties. You do run into a lot of people who want too much money due to what they owe, but there are also reasonable people who don't owe on their trailer and/or know what the realistic value is. I think you can get better deals private party than you can get from a dealer, but it does take more legwork and diligence on your part. I've always just paid cash but I imagine adding any financing to the mix could make it more challenging.
In any case, make sure to closely inspect the unit and be absolutely sure the sellers have good clean title, and make sure the title is exchanged contemporaneously with the cash.