I could see it being legit in the sense that if someone is moving and is in a rush, they would price it at a ridiculous price to have it go. Not that I am financially well off, but I know I do it all the time just to get rid of the stuff quickly.
What I would do is go ahead and ask to go see it and you'll know right away if it's a scam because only a legit seller will set up a visit to this trailer. A scammer will have some good excuse for you not to go see it.
When you've seen it, and are about to pay, before you do call your local police station with the trailer identification number. Make sure it's not a stolen trailer that's being searched for.
I'm getting a feeling that you're not going to be able to go see this trailer tho, something is going to make it "difficult".