It’s nearly impossible to change somebody’s mind. When you try to do so, you’re basically saying: “You were wrong.”
Nobody likes to admit they were wrong. Do you?
Your prospects make their decisions consciously (or unconsciously) based on how much value they feel they’re getting out of the deal. Once a decision is made, they won’t change their minds. At this point, your prospects won’t buy from you, unless you increase the perceived value of the deal.
What’s the solution?
Help your prospects make a new decision with new information. Provide new options, make them aware of other problems they have, tell new stories, explain more benefits, add new guarantees, share testimonials, have one of your current customers recommend you, lower their commitments… 
Your prospects won’t need to think that they made a mistake. They’ll be happy to make a new decision, based on new information.
Notes about Why Prospects Don’t Change Their Minds
 Please note that I didn’t mention “price”. Reducing price is always a bad idea. It can only be your last resort.