As far as selling, it's a nice in between size. The 7K GVWR trailers (tow 3.5K axles, usually only one has brakes) go for $2,500 and up, around here, in similar condition. Yours is a nice size at 12K and brakes on both axles is a nice feature, required for commercial use and for all trailers, in some States. The only things that hurt it are the tires and the short length. Really, it would be good for pulling with a half-ton (not to full GVWR) and would satisfy a lot of commercial needs. I doubt you will have a hard time selling it. I wouldn't take less than $3,000 and you might get closer to $4,000. My guess is you list it for $4,000 and it sells +/-$200 from $3,500.