How Do You Determine How Much Edge There Is in a Trade?

How do you determine, how do you put a dollar value on how much edge there is in a particular trade? Because we're largely relying on the market for information about what fair pricing is. So if i think anoptionis worth a dollar, and i see an offer to sell at 98 cents posted on an exchange that has a half penny removed fee, then i would say, ok, well,there's one point five cents of edge in that opportunity. And that may be good enough, or it may not be good enough,. depending on my peramerizations a on with you.