Asking for a deposit does not mean he is a scammer.
He is taking just as much a risk that he will travel hundreds of miles to pick up your tractor and then being told sorry I changed my mind.
With out a deposit he is SOL.
You are not a business with a track record so look at it from his side for a second.
I have been in this business all my adult life and if I were looking for something to be hauled I would...........
First look for a local hauler. Someone that is local to you should not have a problem showing up without a deposit.
If that did not work out .......
Second I would look for a big company. Many truck lines have smaller what I call hot shot trucks and trailers.
If that was to high or did not work out .....
Third I would look for a small one truck outfit. I would ask for his DOT and MC #'s and look them up Here
From this site I could see what if any insurance he may have and if he has a legal right to haul my tractor across state lines.
I would not have a problem giving any of the above a deposit even though most of the above may not ask for one.
Now if you are looking for a unlicensed; uninsured; guy with a pickup and a trailer trying to make some beer money because he is cheaper than everyone else then maybe a deposit is not such a good idea. He may scam you.