What do most trainers charge to take a horse in for consignment to sell? If they charge a monthly training fee, is the commission different? What about entry fees and hauling? 

Good question.

Seller( Consigner) pays all boarding , training, entry fees, hauling fees etc. when horse sells, 10% of sales price is customary. 

I agree with FLITASTIC 100%.  However I have had a trainer contact me about a horse I had for sale.  He sent his customer and priced that horse 2x what I had on him.  At the time I was a bit mad, however I could have never sold the horse for the price he did.  I was 24 at the time, maturity heals a lot of things.