Based on a couple of phone calls I got before I could delete the CL ad and the big smile on the guy's face that bought my tractor I'm sure I could have gotten $14K and maybe 15K for it. The Kubota was low hours and in tip top shape. The Rhino bush hog was older but heavy duty and in great shape as well. I understand and agree with dealers' overhead, labor costs, etc. I've been self employed before and experienced them myself. What I don't agree with is greed and this dealer was greedy.
I've never heard anybody factor in the income tax the poor old dealer has to pay on his profits. That's a new one on me. If they are so concerned about the income tax they will have to pay on their profit, then they should bump up my trade, thus lowering their tax liability. My dislike (I don't hate anybody) for this dealer is not misplaced at all.
As a side note, this dealership was where I originally purchased the M4900. I traded in a Massey Ferguson on the Kubota and felt like I got an OK deal. Since then the dealership has changed hands, changed names and new owners had taken over. I hear they are not doing well as the family that had it for many, many years. I think I know why.
I dont know your situation and all the facts and figures, so not making judgement on you our your situation. Just putting out there somethings that factor in. Average small business pays 20% in taxes, so taxes are a factor and its nothing to do with a poor business mentality. But by going off what you got your machine sold for 13, that was market for it unless something else happened. Dealer probably then pays his salesman another 5-10% in commission, full tank of gas, machine cleaned, mechanics do a once over possibly change fluid, cost of utilities, insurance all the business overhead factored into what each sale cost him. Break it all down in that manner, there looks to be maybe 2k or so in profit off the trade figures you gave him.