To give a not-to-be-taken-too-seriously example: if we could use Black-Scholes to price options (and agree on volatility etc...) we surely would, but who can hedge continuously? However the BS price would still be the benchmark relative to which any person in the market would consider fair value to be. Obviously that's arbitrage pricing, and although it's not everyone's job description when you price something you have to assume that there is someone, somewhere who will take those risks on and consider themselves adequately compensated for doing so.That last caveat is where (I think) most of us traders come into play, there's often someone somewhere who will pay away a little bit "to get a deal done" be they a fund manager, client, or another bank with a trader who has been stopped out. In my limited experience these are the people who present the best profit opportunities and the best quality (in terms of stability) return.

The purpose of pricing is not(!) to obtain the price. I can always obtain the price by calling up a few friends to quote both sides of the market, and these are generally pretty close unless the deal is real toxic. The purpose of pricing is to obtain the risks, so you can hedge. Hopefully this retains the value of the deal until I can close it out. Black Scholes does not give us the option price, it gives us the price in terms of the volatility; either the dollar price or the vol will be quoted, so the market is giving us the price. But the BS formula tells us how to hedge the option to preserve this value.