If it's the same as motorbikes (i dont know) i got shown a really good trick.
My bike starter motor was temperamental, so put it in gear and roll it forwards in gear till you feel the engine "catch" (resistance of engine) then try again, this can somehow engage the starter motor.
Someone may be along to tell me this wont work but worth a try if your stranded :nenau
you are right mate but rocking mine on the starter wont make a difference I think the starter is knackered