I don't think I ever get this close to a dog to view its expression and make a decision. If the other dog is off lead and moving towards us I now leave Monty off lead too ( assuming we are in relative close proximity, to give Monty the choice to move away)
If I saw this dog up close, and it was still, and I had a choice to put Monty on lead and avoid it, I would.
However, I think this is close to the body language that Monty can portray. He is still, although with tail wagging, sometimes an intense stare, weighing up whether to run towards/ wait/ or roll over another dog approaching him. No hint of aggression- all anticipation, a waiting and weighing up of what rewards an encounter with another dog might bring.